# Obtain IR diffuse data from WISE

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I need some help obtaining IR background diffuse data from the WISE observation. There is already some work done in this regard; see: http://wise.skymaps.info/ . These are .fits files. How do I find out the photon irradiance for a range (say glat b/w 0 and 30) from these files? Any help is appreciated. Also, how do I correlate this with UV flux for the same range using python?

Assuming you have downloaded their software from the link you provided and have astropy installed, you should be able to do:

from wssa_utils import wssa_getval from astropy import units as u from astropy.coordinates import SkyCoord # Declare your wanted point in Galactic co-ordinates c = SkyCoord(l=0, b=30, unit=(u.deg,u.deg), frame="galactic") ra = c.icrs.ra dec = c.icrs.dec vals = wssa_getval(ra, dec)

The results look like they will be in MegaJanskys per steradian, which would beu.MJy/u.srin astropy units. For UV data, I'm not sure what is best, maybe GALEX ?

## Obtain IR diffuse data from WISE - Astronomy

Classification of Galaxies:

It was in the middle of the eighteenth century that Kant and Wright first suggested that the Milky Way represents a finite-sized disk-like system of stars. As an extension of their philosophical argument about the nature of the Galaxy, Kant went on to suggest that if the Milky Way is limited in extent, perhaps the diffuse and very faint "elliptical nebulae" seen in the night sky might actually be extremely distant disk-like systems, similar to our own. He called these objects island universes.

As a first step in understanding any new collection of objects, it is necessary to classify them according to their intrinsic characteristics. Hubble played a major role in this classification. Hubble in his book "The realm of nebulae", Hubble proposed that galaxies be grouped into three primary categories based on their overall appearance. This morphological classification scheme, known as the Hubble sequence, divides galaxies into ellipticals (E's), spirals, and irregulars (Irr's).The spirals are further subdivided into two parallel sequences, the normal spirals (S's), and the barred spirals (SB's). A transitional class of galaxies between ellipticals and spirals is known as lenticulars. It can be either normal (S0's) or barred (SB0's). Hubble then arranged this morphological sequence in the form of a tuning-fork diagram.

Hubble originally thought (incorrectly) that the tuning-fork diagram could be interpreted as an evolutionary sequence for galaxies. As a result, he referred to galaxies toward the left of the diagram as early types and to those toward the right as late types, terminology that is still in widespread use today. Within the category of ellipticals, Hubble made divisions based on the observed ellipticity of the galaxy, defined by

Where α and β are the apparent major and minor axes of the ellipse, respectively, projected onto the plane of the sky. Galaxies with ellipticities greater than ∈=0.7 have never been observed, implying that no E galaxies with intrinsic ellipticities greater than 0.7 appear to exist. The apparent ellipticity may not correspond well to an actual ellipticity since the orientation of the spheroid to our line of sight plays a crucial role in our observations.

This is a spheroidal galaxy that has lengths a=b and c<a.

A prolate spheroidal galaxy has axis lengths b=c and a>b.

Hubble subdivided the spiral sequences into Sa, Sab, Sb, Sbc, Sc, and SBa, SBab,

SBb, SBbc, SBc. The galaxies with the most prominent bulges the largest bulge-to-disk luminosity ratios,(L_bulge⁄(L_disk

0.3)) the most tightly wound spiral arms. and the smoothest distribution of stars in the arms are classified as Sa's (or SBa's), while Sc's (or SBc's) have smaller bulge-to-disk ratios (L_bulge⁄L_disk

0.005) Hubble split the remaining category of irregulars into Irr I if there was at least some hint of an organized structure, such as spiral arms, and Irr II for the most extremely disorganized structures. Hubble split the remaining category of irregulars into Irr I if there was at least some hint of an organized structure, such as spiral arms, and Irr II for the most extremely disorganized structures.

As a further refinement to the system, the lenticular galaxies are also sometimes subdivided according to the amount of dust absorption in their disks. S01 galaxies have no dust their disks, while S03 galaxies have significant amounts of dust, and similarly for SB01 through SB03.In order to make finer distinctions between normal and barred spirals, de Vaucouleurs had also suggested referring to normal spirals as SA rather than simply S. Intermediate types with weak bars are then characterized as SAB, and strongly barred galaxies are SB. The overall picture of classification looks like this

As we all know the galaxies are basically of three types -- Elliptical, Spiral and Irregular.

Elliptical Galaxies (E Galaxy/ Early type Galaxy):

• They have smooth light distributions. The Hubble classifications of these galaxies contain an integer 'n' that describes the elongation of the galaxy image. The classification is determined by the semi major and semi minor axes of the galaxy's isophotes (a line in a diagram connecting points where the intensity of the light is same). It is denoted by En, where

They are given number from 0 to 7. An E0 galaxy looks like a circle whereas an E7 galaxy looks long and elongated.

In a 3D ellipsoidal shape with semi axes a, b, c if:

a=b>c it is called oblate, a>b=c it is called prolate, a>b>c it is called tri-axial.

-They have no current star formation and are usually found in galaxy clusters and compact groups.

-They have old stars and contains little gas and dust.

Spiral Galaxies (S Galaxy/ Late type Galaxy):

Components of S galaxies are spiral arms, bulge, bar, spheroid

They have light profiles with a characteristic spiral spin.

They contain both new and old stars. New stars are formed, especially in the spiral arms.

They seem to avoid dense groups and are very rare in clusters.

NGC 428 Barred Spiral Galaxy

Irregular Galaxies (Irr Galaxy):

It doesn't have a distinct regular shape like spiral or elliptical galaxies and do not fall into any classes of Hubble sequence.

They are usually found in groups or clusters where the collision or near-misses between the galaxies is common.

One type of irregular galaxies is 'Starburst Galaxy'. They shine very brightly as the new stars are born in a short period of time.

Lenticular Galaxies (Armless spiral Galaxy):

They have central bulge but have no spiral arms. If the central bulge is not very bright it will be difficult to differentiate between lenticular galaxy and E0 galaxy.

Few lenticular galaxies have bars like spiral galaxies they are called barred lenticular galaxies and denoted as SB0. Other normal galaxies are denoted as S0.

Application:
Most galaxies can be broadly separated into two morphological types -- spiral and elliptical .Galaxy Zoo was the first attempt to analyze the distribution of a large number of spiral and elliptical galaxies in the local universe. Using the power of crowd sourcing, it provided morphological classifications of nearly 900,000 galaxies. A more recent catalog of galaxy morphology is the catalog of ∼3,000,000 Sloan Digital Sky Survey (SDSS) galaxies classified automatically using machine learning. While the catalog is large, it is limited in the sense that the vast majority of the galaxies in that catalog do not have spectroscopic data.

Photometric redshifts
An area of astrophysics that has greatly increased in popularity in the last few years is the estimation of redshifts from photometric data. This is because, although the distances are less accurate than those obtained with spectra, the sheer number of objects with photometric measurements can often make up for the reduction in individual accuracy by suppressing the statistical noise of an ensemble calculation.
o test machine learning and variable selection algorithms for computing photometric redshift, optimize it for a specific population of galaxies, and mainly apply these algorithms to provide a large catalog of galaxy morphology and photometric redshift. The catalog is similar to the early Galaxy Zoo 1 catalog, but because it was classified automatically it provides a much higher number of galaxies. Of the ∼ 3 - 106 galaxies in the catalog, ∼ 1.5 - 106 are galaxies with 98% agreement rate with the Galaxy Zoo 1 debiased "super clean" accuracy. It is limited in the sense that, like Galaxy Zoo, it represents the galaxies in the catalog, and not necessarily a complete and unbiased sample of SDSS galaxies. The catalog is publicly available at:

At low redshifts, the calculation of photometric redshifts for normal galaxies is quite straightforward due to the break in the typical galaxy spectrum at 4000A. Thus, as a galaxy is redshifted with increasing distance, the color (measured as a difference in magnitudes) changes relatively smoothly. As a result, both template and empirical photo-z approaches obtain similar results, a root-mean-square deviation of

0.02 in redshift, which is close to the best possible result given the intrinsic spread in the properties

Historically, the calculation of photometric redshifts for quasars and other AGN has been even more difficult than for galaxies, because the spectra are dominated by bright but narrow emission lines, which in broad photometric pass bands can dominate the color. The color-redshift relation of quasars is thus subject to several effects, including degeneracy, one emission line appearing like another at a different redshift, an emission line disappearing between survey filters, and reddening. In addition, the filter sets of surveys are generally designed for normal galaxies and not quasars. The assignment of these quasar photo-zs is thus a complex problem that is amenable to data mining in a similar manner to the classification of AGN.

Other Galaxy Classifications
Many of the physical properties, and thus classification, of a galaxy are determined by its stellar population. The spectrum of a galaxy is therefore another method for classification and can sometimes produce a clearer link to the underlying physics than the morphology. Spectral classification is important because it is possible for a range of morphological types to have the same spectral type, and vice versa, because spectral types are driven by different underlying physical processes.

Galaxies come in a range of different sizes and shapes, or more collectively, morphology. The most well-known system for the morphological classification of galaxies is the Hubble Sequence of elliptical, spiral, barred spiral, and irregular, along with various subclasses. This system correlates to many physical properties known to be important in the formation and evolution of galaxies.

Recently, the popular Galaxy Zoo project has taken an alternative approach to morphological classification, employing crowd sourcing: an application was made available online in which members of the general public were able to view images from the SDSS and assign classifications according to an outlined scheme. The project was very successful, and in a period of six months over 100,000 people provided over 40 million classifications for a sample of 893,212 galaxies, mostly to a limiting depth of r = 17.77 mag. The classifications included categories not previously assigned in astronomical data mining studies, such as edge-on or the handedness of spiral arms, and the project has produced multiple scientific results. The approach represents a complementary one to automated algorithms, because, although humans can see things an algorithm will miss and will be subject to different systematic errors, the runtime is hugely longer: a trained ANN will produce the same 40 million classifications in a few minutes, rather than six months.

• Statistical inference and visualization with very-large-N datasets represents a scientific and technological framework needed to cope with this data flood. Considerable work is being conducted by computer scientists and applied mathematicians in other applied fields so that independent development by astro-statisticians might not be necessary to achieve certain goals.

Aside from the computational challenges with large numbers of data vectors and a large dimensionality, this poses some highly non-trivial statistical problems. The problems are driven not just by the size of the data sets, but mainly (in the statistical context) by the heterogeneity and intrinsic complexity of the data.

Astrophysicists often devote as much effort to precise determination of their errors as they devote to the measurements of the quantities of interest. The instruments are carefully calibrated to reduce systematic uncertainties, and background levels and random fluctuations are carefully evaluated to determine random errors.

Bayes Theorem and Bayes factors are becoming increasingly well known in astronomical research. Part of the problem is conceptual astronomers need training in how to construct likelihoods for familiar parametric situations.

Wavelet analysis suffers a profound limitation in astronomy

Application of the redshift-distance relation (Hubble's law) allows the analysis of the largescale distribution of galaxies. Comparison of the observed redshifts with those expected on the basis of other distance estimates allows mapping of the gravitational field and the underlying density distribution. Estimation of the many inherent selection biases and instrumental limitations is critical in understanding how our view of the universe is affected by our observational perspective and by the way information is received by current technologies.

The current state of play with regard to correlation function analysis, both in terms of computational and sampling problems and with regard to the fundamental limitations of such an approach in giving a complete statistical description of the pattern. Various techniques have been devised to attempt to quantify the topology of the clustering pattern with varying degrees of success.

The lack of adequate cluster samples to provide an unbiased look at the problem, the lack of supplemental data in most clusters to confirm or reject possible small-scale structures.

## Obtain IR diffuse data from WISE - Astronomy

Using data from the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite, we made a catalog of over 8000 Galactic HII regions and HII region candidates by searching for their characteristic mid-infrared (MIR) morphology. WISE has sufficient sensitivity to detect the MIR emission from HII regions located anywhere in the Galactic disk. We believe this is the most complete catalog yet of regions forming massive stars in the Milky Way. Of the

1500 have measured radio recombination line (RRL) or H-alpha emission, and are thus known to be HII regions. This sample improves on previous efforts by resolving HII region complexes into multiple sources and by removing duplicate entries. There are

2500 candidate HII regions in the catalog that are spatially coincident with radio continuum emission. Our group's previous RRL studies show that

95% of such targets are HII regions. We find that

500 of these candidates are also positionally associated with known HII region complexes, so the probability of their being bona fide HII regions is even higher. At the sensitivity limits of existing surveys,

4000 catalog sources show no radio continuum emission. Using data from the literature, we find distances for

1500 catalog sources, and molecular velocities for

1500 HII region candidates.

Finding Distant Galactic HII Regions ADS pdf Abstract

The WISE Catalog of Galactic HII Regions contains

2000 HII region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic HII region mid-infrared morphology of WISE 12µm emission surrounding 22µm emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line and radio continuum detections in the X-band (9 GHz 3 cm) of 302 WISE HII region candidates (out of 324 targets observed) in the zone 225° ≥ l ≥ -20°, |b| ≤ 6° Here we extend the sky coverage of our HII region Discovery Survey, which now contains nearly 800 HII regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have (l,b,v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1° in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422 -54.9 km/s). With Heliocentric distances >22 kpc and Galactocentric distances >16 kpc, the OSC HII regions are the most distant known in the Galaxy. We detect an additional three HII regions near l=150° whose LSR velocities place them at Galactocentric radii >19 kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.

The Infrared and Radio Flux Densities of Galactic HII regions ADS pdf Abstract

We derive infrared and radio flux densities of all

1000 known Galactic HII regions in the Galactic longitude range 17.5° l > -20° at b = 0° All sources were selected from the WISE Catalog of Galactic HII Regions, and have infrared angular diameters >260''. The Galactic distribution of these "large" HII regions is similar to that of the previously-known sample of Galactic HII regions. The large HII region RRL line width and peak line intensity distributions are skewed toward lower values compared with that of previous HRDS surveys. We discover 7 sources with extremely narrow RRLs 100 pc, making them some of the physically largest known HII regions in the Galaxy. This survey completes the HRDS HII region census in the Northern sky, where we have discovered 887 HII regions and more than doubled the previously-known census of Galactic HII regions.

The Southern HII Region Discovery Survey (SHRDS): Pilot Survey ADS pdf Abstract

The Southern HII Region Discovery Survey is a survey of the third and fourth quadrants of the Galactic plane that will detect radio recombination line (RRL) and continuum emission at cm-wavelengths from several hundred HII region candidates using the Australia Telescope Compact Array. The targets for this survey come from the WISE Catalog of Galactic HII Regions and were identified based on mid-infrared and radio continuum emission. In this pilot project, two different configurations of the Compact Array Broad Band receiver and spectrometer system were used for short test observations. The pilot surveys detected RRL emission from 36 of 53 HII region candidates, as well as seven known HII regions that were included for calibration. These 36 recombination line detections confirm that the candidates are true HII regions and allow us to estimate their distances.

A Galactic Plane Defined by the Milky Way HII Region Distribution ADS pdf Abstract

We develop a framework for a new definition of the Galactic midplane, allowing for tilt (&thetatilt) rotation about Galactic azimuth 90°) and roll (&thetaroll) rotation about Galactic azimuth 0°) of the midplane with respect to the current definition. Derivation of the tilt and roll angles also determines the solar height above the midplane. Here we use nebulae from the Wide-field Infrared Survey Explorer (WISE) Catalog of Galactic HII Regions to define the Galactic high-mass star formation (HMSF) midplane. We analyze various subsamples of the WISE catalog and find that all have Galactic latitude scale heights near 0.30° and z-distribution scale heights near 30 pc. The vertical distribution for small (presumably young) HII regions is narrower than that of larger (presumably old) HII regions (

40 pc), implying that the larger regions have migrated further from their birth sites. For all HII region subsamples and for a variety of fitting methodologies, we find that the HMSF midplane is not significantly tilted or rolled with respect to the currently defined midplane, and, therefore, the Sun is near to the HMSF midplane. These results are consistent with other studies of HMSF, but are inconsistent with many stellar studies, perhaps because of asymmetries in the stellar distribution near the Sun. Our results are sensitive to latitude restrictions and also to the completeness of the sample, indicating that similar analyses cannot be done accurately with less complete samples. The midplane framework we develop can be used for any future sample of Galactic objects to redefine the midplane.

The Southern HII Region Discovery Survey. I. The Bright Catalog ADS pdf Abstract

The census of Galactic HII regions is vastly incomplete in the southern sky. We use the Australia Telescope Compact Array to observe 4-10 GHz radio continuum and hydrogen radio recombination line (RRL) emission from candidate HII regions in the Galactic zone 259°

## Runaway Stars Leave Infrared Waves in Space

Astronomers are finding dozens of the fastest stars in our galaxy with the help of images from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE.

When some speedy, massive stars plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship. Called bow shocks, these dramatic arc-shaped features in space are leading researchers to uncover massive, so-called runaway stars.

"Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters," said astronomer William Chick from the University of Wyoming in Laramie, who presented his team's new results at the American Astronomical Society meeting in Kissimmee, Florida. "The gravitational boost increases a star's speed relative to other stars."

Our own Sun is strolling through our Milky Way galaxy at a moderate pace. It is not clear whether our Sun creates a bow shock. By comparison, a massive star with a stunning bow shock, called Zeta Ophiuchi (or Zeta Oph), is traveling around the galaxy faster than our Sun, at 54,000 mph (24 kilometers per second) relative to its surroundings. Zeta Oph's giant bow shock can be seen in the accompanying image from the WISE mission.

Both the speed of stars moving through space and their mass contribute to the size and shapes of bow shocks. The more massive a star, the more material it sheds in high-speed winds. Zeta Oph, which is about 20 times as massive as our Sun, has supersonic winds that slam into the material in front of it.

The result is a pile-up of material that glows. The arc-shaped material heats up and shines with infrared light. That infrared light is assigned the color red in the many pictures of bow shocks captured by Spitzer and WISE.

Chick and his team turned to archival infrared data from Spitzer and WISE to identify new bow shocks, including more distant ones that are harder to find. Their initial search turned up more than 200 images of fuzzy red arcs. They then used the Wyoming Infrared Observatory, near Laramie, to follow up on 80 of these candidates and identify the sources behind the suspected bow shocks. Most turned out to be massive stars.

The findings suggest that many of the bow shocks are the result of speedy runaways that were given a gravitational kick by other stars. However, in a few cases, the arc-shaped features could turn out to be something else, such as dust from stars and birth clouds of newborn stars. The team plans more observations to confirm the presence of bow shocks.

"We are using the bow shocks to find massive and/or runaway stars," said astronomer Henry "Chip" Kobulnicky, also from the University of Wyoming. "The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars."

Another group of researchers, led by Cintia Peri of the Argentine Institute of Radio Astronomy, is also using Spitzer and WISE data to find new bow shocks in space. Only instead of searching for the arcs at the onset, they start by hunting down known speedy stars, and then they scan them for bow shocks.

"WISE and Spitzer have given us the best images of bow shocks so far," said Peri. "In many cases, bow shocks that looked very diffuse before, can now be resolved, and, moreover, we can see some new details of the structures."

Some of the first bow shocks from runaway stars were identified in the 1980s by David Van Buren of NASA's Jet Propulsion Laboratory in Pasadena, California. He and his colleagues found them using infrared data from the Infrared Astronomical Satellite (IRAS), a predecessor to WISE that scanned the whole infrared sky in 1983.

Kobulnicky and Chick belong to a larger team of researchers and students studying bow shocks and massive stars, including Matt Povich from the California State Polytechnic University, Pomona. The National Science Foundation funds their research.

Images from Spitzer, WISE and IRAS are archived at the NASA Infrared Science Archive housed at the Infrared Processing and Analysis Center at California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

## Mysterious Signal comes from very Old Stars at the centre of the Milky Way

The gravity from ordinary matter – stars, interstellar gas and dust - alone is not sufficient to keep Galaxies from falling apart. An abundance of roughly five times as much Dark Matter as ordinary matter is needed to hold Galaxies together. It is now well established that the Galaxy which we inhabit, the Milky Way, is embedded in an enormous spherically shaped clump or “halo” of this strange substance.

Illustration of the structure of the Milky Way: The bright visible disk of stars and gas is embedded in a large, roughly spherical dark matter halo. Densities of both visible and dark matter rise towards the Galactic centre, where there is also an extended bulge of stars. [Image credit:L. Jaramillo & O. Macias/Virginia Tech.]

Unlike most ordinary matter, Dark Matter particles are invisible to optical telescopes, but may smash against each other and radiate gamma-ray photons a billion times more energetic than visible light. Such a glow of Dark Matter emission is expected to be brightest at the Centre of the Milky Way due to the very high concentration of Dark Matter particles in that region of the sky.

The Fermi Gamma-Ray Space Telescope (launched in 2008 and still in operation) has allowed scientists to have the clearest ever view of the gamma-ray sky at the few giga-electron volt energy range. In one of the most interesting recent developments in our quest for Dark Matter, several independent studies of Fermi Satellite data uncovered a mysterious gamma-ray signal originating from the Galactic Centre (hereafter Fermi Galactic Centre excess) that was easily accommodated by some of the best theoretically motivated Dark Matter models.

The Fermi Gamma-Ray Space Telescope scans the full sky every 3 hours detecting photons about 1 billion times more energetic than visible light. [Images Credit: NASA/Aurore Simonnet, Sonoma State University. Photo-illustration: Sandbox Studio]

The centre of our Galaxy may be rich in Dark Matter, but it is also rich in stars. As shown in the artistic illustration below, the stars of the Milky Way are distributed in three main structures: a central bulge, a dominant disk and a diffuse stellar halo. N-body simulations show that the Milky Way bulge was formed through an entangled process of stellar orbit evolution - disk stars originally orbiting in the plane of the Galaxy slowly transition to bulge orbits via dynamical instabilities. The instantaneous spatial distribution of the bulge stars results in bulge shapes that can be distinctively non-spherical.

Artist's illustration of the main stellar structures of the Milky Way Galaxy. The bulge stars are distinctively non-spherical. Our new study compares maps of the various stellar populations of the Galactic bulge against the spatial distribution of the Fermi Galactic centre excess data. [Credit: L. Jaramillo & O. Macias/Virginia Tech.]

Near infrared data from the Diffuse Infrared Background Experiment instrument on board the COBE satellite first established the non-spherical nature of the Milky Way bulge. This was later confirmed by stellar count maps of different surveys (e.g. 2MASS, OGLE-II and VVV survey). The image below displays new diffuse infrared measurements taken with NASA's Wide-field Infrared Survey Explorer (WISE), which reveals the non-spherical morphology of the bulge stars.

Image of the central regions of the Milky Way taken with the NASA infrared space telescope WISE. The spatial distribution of the bulge stars differs from a spherical shape. Our analysis uses stellar maps obtained with WISE and COBE/DIRBE data, among others. [Image credit: NASA/JPL-Caltech/D.]

Our new study, recently confirmed by an independent team, shows that there is a detailed match between the projected maps of various stellar populations of the Galactic bulge and the spatial morphology of the Fermi Galactic Centre excess signal. This finding essentially requires that an astrophysical source connected to these stars is responsible for the Galactic centre gamma-ray excess and rules out a Dark Matter explanation of the signal.

## Spitzer and WISE Reveal Dozens of Runaway Stars

Bow shocks thought to mark the paths of massive, speeding stars are highlighted in these images from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE. Green shows wispy dust in the region and blue shows stars. The two images at left are from Spitzer, and the one on the right is from WISE. The speeding stars thought to be creating the bow shocks can be seen at the center of each arc-shaped feature. The image at right actually consists of two bow shocks and two speeding stars. All the speeding stars are massive, ranging from about 8 to 30 times the mass of our sun.

Using NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer, astronomers are finding dozens of the fastest stars in our galaxy.

When some speedy, massive stars plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship. Called bow shocks, these dramatic, arc-shaped features in space are leading researchers to uncover massive, so-called runaway stars.

“Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters,” said astronomer William Chick from the University of Wyoming in Laramie, who presented his team’s new results at the American Astronomical Society meeting in Kissimmee, Florida. “The gravitational boost increases a star’s speed relative to other stars.”

Our own sun is strolling through our Milky Way galaxy at a moderate pace. It is not clear whether our sun creates a bow shock. By comparison, a massive star with a stunning bow shock, called Zeta Ophiuchi (or Zeta Oph), is traveling around the galaxy faster than our sun, at 54,000 mph (24 kilometers per second) relative to its surroundings.

Both the speed of stars moving through space and their mass contribute to the size and shapes of bow shocks. The more massive a star, the more material it sheds in high-speed winds. Zeta Oph, which is about 20 times as massive as our sun, has supersonic winds that slam into the material in front of it.

The result is a pile-up of material that glows. The arc-shaped material heats up and shines with infrared light. That infrared light is assigned the color red in the many pictures of bow shocks captured by Spitzer and WISE.

Chick and his team turned to archival infrared data from Spitzer and WISE to identify new bow shocks, including more distant ones that are harder to find. Their initial search turned up more than 200 images of fuzzy red arcs. They then used the Wyoming Infrared Observatory, near Laramie, to follow up on 80 of these candidates and identify the sources behind the suspected bow shocks. Most turned out to be massive stars.

The findings suggest that many of the bow shocks are the result of speedy runaways that were given a gravitational kick by other stars. However, in a few cases, the arc-shaped features could turn out to be something else, such as dust from stars and birth clouds of newborn stars. The team plans more observations to confirm the presence of bow shocks.

“We are using the bow shocks to find massive and/or runaway stars,” said astronomer Henry “Chip” Kobulnicky, also from the University of Wyoming. “The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars.”

Another group of researchers, led by Cintia Peri of the Argentine Institute of Radio Astronomy, is also using Spitzer and WISE data to find new bow shocks in space. Only instead of searching for the arcs at the onset, they start by hunting down known speedy stars, and then they scan them for bow shocks.

“WISE and Spitzer have given us the best images of bow shocks so far,” said Peri. “In many cases, bow shocks that looked very diffuse before, can now be resolved, and, moreover, we can see some new details of the structures.”

Some of the first bow shocks from runaway stars were identified in the 1980s by David Van Buren of NASA’s Jet Propulsion Laboratory in Pasadena, California. He and his colleagues found them using infrared data from the Infrared Astronomical Satellite (IRAS), a predecessor to WISE that scanned the whole infrared sky in 1983.

Kobulnicky and Chick belong to a larger team of researchers and students studying bow shocks and massive stars, including Matt Povich from the California State Polytechnic University, Pomona. The National Science Foundation funds their research.

## Contents

The Italian astronomer Paolo Maffei was one of the pioneers of infrared astronomy. In the 1950s and 60s, in order to obtain high quality images of celestial objects in the very near infrared part of the spectrum (the I-band, 680–880 nm), he used chemically hyper-sensitized standard Eastman emulsions I-N. [note 1] To achieve the hyper-sensitization he immersed them in 5% ammonia solution for 3–5 minutes. This procedure increased their sensitivity by an order of magnitude. Between 1957 and 1967 Maffei observed many different objects using this technique, including globular clusters and planetary nebulae. Some of those objects were not visible at all on blue light (250–500 nm) sensitive plates. [6]

The galaxy Maffei 1 was discovered on a hyper-sensitized I-N photographic plate exposed on 29 September 1967 with the Schmidt telescope at Asiago Observatory. Maffei found Maffei 1, together with its companion spiral galaxy Maffei 2, while searching for diffuse nebulae and T Tauri stars. [2] The object had an apparent size up to 50″ in the near infrared but was not visible on the corresponding blue light sensitive plate. [7] Its spectrum lacked any emission or absorption lines. Later it was shown to be radio-quiet as well. In 1970 Hyron Spinrad suggested that Maffei 1 is a nearby heavily obscured giant elliptical galaxy. [8] Maffei 1 would be among the ten brightest galaxies in the northern sky if not situated behind the Milky Way. [6]

Maffei 1 is located only 0.55° from the galactic plane in the middle of the zone of avoidance and suffers from about 4.7 magnitudes of extinction (a factor of about 1/70) in visible light. In addition to extinction, observation of Maffei 1 is further hindered by the fact that it is covered by myriads of faint Milky Way stars, which can easily be confused with its own. As a result, determining its distance has been particularly difficult. [2]

In 1971, soon after its discovery, Hyron Spinrad estimated the distance to Maffei 1 at about 1 Mpc, which would place it within the Local Group of galaxies. In 1983 this estimate was revised up to 2.1 +1.3
−0.8 Mpc by Ronald Buta and Marshall McCall using the general relation between the luminosity and velocity dispersion for elliptical galaxies. [2] That distance puts Maffei 1 well outside the Local Group, but close enough to have influenced it in the past. [4]

In 1993 Gerard Luppino and John Tonry used surface brightness fluctuations to derive a new distance estimate to Maffei 1 of 4.15 ± 0.5 Mpc . Later in 2001, Tim Davidge and Sidney van den Bergh used adaptive optics to observe the brightest asymptotic giant branch stars in Maffei 1 and concluded that it is located at the distance 4.4 +0.6
−0.5 Mpc from the Sun. [4] [2] The latest determination of the distance to Maffei 1, which is based on the re-calibrated luminosity/velocity dispersion relation for the elliptical galaxies and the updated extinction, is 2.85 ± 0.36 Mpc , or over 9 million light years away. For perspective, the nearby Andromeda Galaxy is estimated to be about 2.5 million light years away.

The larger (≥3 Mpc) distances reported in the past 20 years would imply that Maffei 1 has never been close enough to the Local Group to significantly influence its dynamics. [3]

Maffei 1 moves away from the Sun at the speed of about 66 km/s. [2] Its velocity relative to the Local Group's center of mass is, however, 297 km/s away. That means that Maffei 1 participates in the general expansion of the Universe. [9]

### Size and shape Edit

Maffei 1 is a massive elliptical galaxy classified as type E3 in the Hubble classification scheme. [10] This means that it is slightly flattened, its semi-minor axis being 70% of its semi-major axis. Maffei 1 has also a boxy shape (E(b)3 type), while its central region (radius ≈ 34 pc) is deficient in light emission as compared to the r 1/4 law, [note 2] meaning that Maffei 1 is a core type elliptical. Both the boxy shape and the presence of an underluminous core are typical of intermediate to massive ellipticals. [11]

The apparent dimensions of Maffei 1 depend strongly on the wavelength of light because of the heavy obscuration by the Milky Way. In blue light it is 1–2′ across while in the near infrared its major axis reaches 23′—more than 3/4 of the Moon's diameter. At a distance of 3 Mpc this corresponds to approximately 23 kpc. [10] The total visible absolute magnitude of Maffei 1, MV=−20.8, is comparable to that of the Milky Way. [3]

### Nucleus Edit

Maffei 1 possesses a tiny blue nucleus at its center approximately 1.2 pc across. It contains about 29 solar masses of ionized hydrogen. [11] This implies that it has undergone recent star formation. There are no signs of an active galactic nucleus (AGN) in the center of Maffei 1. The X-ray emission from the center is extended and likely comes from a number of stellar sources. [12]

### Stars and stellar clusters Edit

Maffei 1 is mainly made of old metal-rich stars more than 10 billion years in age. [12] As a large elliptical galaxy, Maffei 1 is expected to host a significant population of globular clusters (about 1100). However, due to heavy intervening absorption, ground-based observations for a long time failed to identify any of them. [12] Observations by the Hubble Space Telescope in 2000 revealed about 20 globular cluster candidates in the central region of the galaxy. [11] Later infrared observations from telescopes on the ground also found a population of bright globular cluster candidates. [13]

Maffei 1 is a principal member of a nearby group of galaxies. The group's other members are the giant spiral galaxies IC 342 and Maffei 2. Maffei 1 has also a small satellite spiral galaxy Dwingeloo 1 as well as a number of dwarf satellites like MB1. The IC 342/Maffei Group is one of the closest galaxy groups to the Milky Way galaxy. [9]

## Obtain IR diffuse data from WISE - Astronomy

To accurately determine the distances to Galactic classical Cepheids in near-IR bands, a sample of Galactic classical Cepheids with near-IR J, H, Ks-band mean magnitudes has been collected from the literature. van Leeuwen+ (2007MNRAS.379..723V) published 229 Cepheids with near-IR mean magnitudes in the South African Astronomical Observatory (SAAO) system. A sample of Galactic Cepheids with individual Baade-Wesselink distances was compiled from Fouque+ (2007, J/A+A/476/73), Groenewegen (2008A&A. 488. 25G), Pedicelli+ (2010A&A. 518A..11P), and Storm+ (2011, J/A+A/534/A94). Monson & Pierce (2011, J/ApJS/193/12) provided near-IR photometric measurements for 131 northern Galactic classical Cepheids. Chen+ (2017MNRAS.464.1119C) used 31 open-cluster Cepheids to obtain JHKs Galactic Cepheid PL relations. After removing duplicate sources, our final sample comprises 288 classical Cepheids. J,H,Ks-band mean magnitudes in the SAAO and European Southern Observatory systems were converted to the Two Micron All Sky Survey (2MASS) system. See section 2 for further explanations.

We take the WISE photometric data of our Cepheid sample from the AllWISE Multi-epoch Photometry Database. The Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) program is a mid-IR survey in four bands ([3.6], [4.5], [5.8], and [8.0]) using the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope. The isophotal central wavelengths are 3.550, 4.439, 5.731, and 7.872um, respectively. The survey data include Spitzer observations from a number of programs covering the Galactic plane: GLIMPSE I, GLIMPSE II, GLIMPSE 3D, GLIMPSE 360, Vela-Carina, Deep GLIMPSE, SMOG, and Cygnus-X (Benjamin+ 2003PASP..115..953B Churchwell+ 2009PASP..121..213C). We search all catalogs for photometric data of our sample Cepheids. In addition, Monson et al. (2012, J/ApJ/759/14) used 37 Galactic Cepheids with Spitzer/IRAC [3.6] and [4.5]-band photometric measurements to calibrate the Galactic Cepheid PL relations. See section 3 for further explanations.

## Contents

The Cosmic Background Explorer (COBE) mission was launched in November 1989. The spacecraft contained liquid helium that cooled the DIRBE instrument to below 2K to allow it to image in the infrared wavelengths. Primary observation started December 11, 1989 and ran until September 21, 1990, when the liquid helium ran out. After that date only observations in the 1.25 to 4.9 micrometer bands could be carried out, at about 20% of original sensitivity. ΐ]

The DIRBE instrument was an absolute radiometer with an off-axis folded-Gregorian reflecting telescope, with 19 cm diameter aperture. Ώ]

## X Marks the Spot for Milky Way Formation

A new understanding of our galaxy's structure began in an unlikely way: on Twitter.

A new understanding of our galaxy's structure began in an unlikely way: on Twitter. A research effort sparked by tweets led scientists to confirm that the Milky Way's central bulge of stars forms an "X" shape. The newly published study uses data from NASA's Wide-field Infrared Survey Explorer (WISE) mission.

The unconventional collaboration started in May 2015 when Dustin Lang, an astronomer at the Dunlap Institute of the University of Toronto, posted galaxy maps to Twitter, using data from WISE's two infrared surveys of the entire sky in 2010. Infrared light allows astronomers to see the structures of galaxies in spite of dust, which blocks crucial details in visible light. Lang was using the WISE data in a project to map the web of galaxies far outside our Milky Way, which he made available through an interactive website.

But it was the Milky Way's appearance in the tweets that got the attention of other astronomers. Some chimed in about the appearance of the bulge, a football-shaped central structure that is three-dimensional compared to the galaxy's flat disk. Within the bulge, the WISE data seemed to show a surprising X structure, which had never been as clearly demonstrated before in the Milky Way. Melissa Ness, a postdoctoral researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany, recognized the significance of the X shape, and contacted Lang.

The two met a few weeks later at a conference in Michigan, and decided to collaborate on analyzing the bulge using Lang's WISE maps. Their work resulted in a new study published in the Astronomical Journal confirming an X-shaped distribution of stars in the bulge.

"The bulge is a key signature of formation of the Milky Way," said Ness, the study's lead author. "If we understand the bulge we will understand the key processes that have formed and shaped our galaxy."

The Milky Way is an example of a disk galaxy -- a collection of stars and gas in a rotating disk. In these kinds of galaxies, when the thin disk of gas and stars is sufficiently massive, a "stellar bar" may form, consisting of stars moving in a box-shaped orbit around the center. Our own Milky Way has a bar, as do nearly two-thirds of all nearby disk galaxies.

Over time, the bar may become unstable and buckle in the center. The resulting "bulge" would contain stars that move around the galactic center, perpendicular to the plane of the galaxy, and in and out radially. When viewed from the side, the stars would appear distributed in a box-like or peanut-like shape as they orbit. Within that structure, according to the new study, there is a giant X-shaped structure of stars crossing at the center of the galaxy.

A bulge can also form when galaxies merge, but the Milky Way has not merged with any large galaxy in at least 9 billion years.

"We see the boxy shape, and the X within it, clearly in the WISE image, which demonstrates that internal formation processes have driven the bulge formation," Ness said. "This also reinforces the idea that our galaxy has led a fairly quiet life, without major merging events since the bulge was formed, as this shape would have been disrupted if we had any major interactions with other galaxies."

The Milky Way's X-shaped bulge had been reported in previous studies. Images from the NASA Cosmic Background Explorer (COBE) satellite's Diffuse Infrared Background Experiment suggested a boxy structure for the bulge. In 2013, scientists at the Max Planck Institute for Extraterrestrial Physics published 3-D maps of the Milky Way that also included an X-shaped bulge, but these studies did not show an actual image of the X shape. Ness and Lang's study uses infrared data to show the clearest indication yet of the X shape.

Additional research is ongoing to analyze the dynamics and properties of the stars in the Milky Way's bulge.

Collaborating on this study was unusual for Lang -- his expertise is in using computer science to understand large-scale astronomical phenomena, not the dynamics and structure of the Milky Way. But he was able to enter a new field of research because he posted maps to social media and used openly accessible WISE data.

"To me, this study is an example of the interesting, serendipitous science that can come from large data sets that are publicly available," he said. "I'm very pleased to see my WISE sky maps being used to answer questions that I didn't even know existed."

NASA's Jet Propulsion Laboratory, Pasadena, California, manages and operates WISE for NASA's Science Mission Directorate in Washington. The spacecraft was put into hibernation mode in 2011, after it scanned the entire sky twice, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.