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Register a new userSpitzer observations of Abell 1763 - I: infrared and optical photometry
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We present a photometric analysis of the galaxy cluster Abell 1763 at visible and infrared wavelengths. Included are fully reduced images in r, J, H, and Ks obtained using the Palomar 200in telescope, as well as the IRAC and MIPS images from Spitzer. The cluster is covered out to approximately 3 virial radii with deep 24um imaging (a 5? depth of 0.2 mJy). This same field of 40 by 40 is covered in all four IRAC bands as well as the longer wavelength MIPS bands (70 and 160um). The r imaging covers 0.8 deg2 down to 25.5 magnitudes, and overlaps with most of the MIPS field of view. The J, H, Ks images cover the cluster core and roughly half of the filament galaxies, which extend towards the neighboring cluster, Abell 1770. This first, in a series of papers on Abell 1763, discusses the data reduction methods and source extraction techniques used for each dataset. We present catalogs of infrared (IR) sources (with 24 and/or 70um emission) and their corresponding emission in the optical (u, g, r, i, z), and Near- to Far-IR (J, H, Ks, IRAC, and MIPS 160um). We provide the catalogs and reduced images to the community through the NASA/IPAC Infrared Science Archive (IRSA).
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The Abell 1763 superstructure at z=0.23 contains the first galaxy filament to be directly detected using mid-infrared observations. Our previous work has shown that the frequency of starbursting galaxies, as characterized by 24{mu}m emission is much higher within the filament than at either the center of the rich galaxy cluster, or the field surrounding the system. New VLA and XMM-Newton data are presented here. We use the radio and X-ray data to examine the fraction and location of active galaxies, both active galactic nuclei (AGN) and starbursts. The radio far-infrared correlation, X-ray point source location, IRAC colors, and quasar positions are all used to gain an understanding of the presence of dominant AGN. We find very few MIPS-selected galaxies that are clearly dominated by AGN activity. Most radio selected members within the filament are starbursts. Within the supercluster, 3 of 8 spectroscopic members detected both in the radio and in the mid-infrared are radio-bright AGN. They are found at or near the core of Abell 1763. The five starbursts are located further along the filament. We calculate the physical properties of the known wide angle tail (WAT) source which is the brightest cluster galaxy (BCG) of Abell 1763. A second double lobe source is found along the filament well outside of the virial radius of either cluster. The velocity offset of the WAT from the X-ray centroid, and the bend of the WAT in the intracluster medium (ICM) are both consistent with ram pressure stripping, indicative of streaming motions along the direction of the filament. We consider this as further evidence of the cluster-feeding nature of the galaxy filament.
We create a model for recovering the intrinsic, absorption-corrected surface brightness distribution of a galaxy and apply the model to the M31. We construct a galactic model as a superposition of axially symmetric stellar components and a dust disc to analyse the intrinsic absorption efects. Dust column density is assumed to be proportional to the far-infrared flux of the galaxy. Along each line of sight, the observed far-infrared spectral energy distribution is approximated with modified black body functions considering dust components with different temperatures, allowing to determine the temperatures and relative column densities of the dust components. We apply the model to the nearby galaxy M31 using the Spitzer Space Telescope far-infrared observations for mapping dust distribution and temperature. A warm and a cold dust component are distinguished. The temperature of the warm dust in M31 varies between 56 and 60 K and is highest in the spiral arms; the temperature of the cold component is mostly 15-19 K and rises up to about 25 K at the centre of the galaxy. The intensity-weighted mean temperature of the dust decreases from T ~32 K at the centre to T ~20 K at R ~7 kpc and outwards. We also calculate the intrinsic UBVRIL surface brightness distributions and the spatial luminosity distribution. The intrinsic dust extinction in the V-colour rises from 0.25 mag at the centre to 0.4-0.5 mag at R = 6-13 kpc and decreases smoothly thereafter. The calculated total extinction-corrected luminosity of M31 is L_B = (3.64 pm 0.15) 10^10L_sun, corresponding to an absolute luminosity M_B = (-20.89 pm 0.04) mag. Of the total B-luminosity, 20% (0.24 mag) is obscured from us by the dust inside M31. The intrinsic shape of the bulge is slightly prolate in our best-fit model.
The survey description and the near-, mid-, and far-infrared flux properties are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a Spitzer Space Telescope legacy program that surveys the local universe out to 11 Mpc, built upon a foundation of ultraviolet, H-alpha, and HST imaging from 11HUGS (11 Mpc H-alpha and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby Galaxy Survey Treasury). LVL covers an unbiased, representative, and statistically robust sample of nearby star-forming galaxies, exploiting the highest extragalactic spatial resolution achievable with Spitzer. As a result of its approximately volume-limited nature, LVL augments previous Spitzer observations of present-day galaxies with improved sampling of the low-luminosity galaxy population. The collection of LVL galaxies shows a large spread in mid-infrared colors, likely due to the conspicuous deficiency of 8um PAH emission from low-metallicity, low-luminosity galaxies. Conversely, the far-infrared emission tightly tracks the total infrared emission, with a dispersion in their flux ratio of only 0.1 dex. In terms of the relation between infrared-to-ultraviolet ratio and ultraviolet spectral slope, the LVL sample shows redder colors and/or lower infrared-to-ultraviolet ratios than starburst galaxies, suggesting that reprocessing by dust is less important in the lower mass systems that dominate the LVL sample. Comparisons with theoretical models suggest that the amplitude of deviations from the relation found for starburst galaxies correlates with the age of the stellar populations that dominate the ultraviolet/optical luminosities.
We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate Active Galactic Nuclei (AGN) selected in the mid-infrared. This survey selects both normal and obscured AGN closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L_bol~10^10L_sun, to highly luminous quasars (L_bol~10^14L_sun), and with redshifts from 0-4.3. Samples of candidate AGN were selected through mid-infrared color cuts at several different 24 micron flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGN and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type-1 AGN with blue continua, 294 (44%) are type-2 objects with extinctions A_V>~5 towards their AGN, 96 (14%) are AGN with lower extinctions (A_V~1) and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. 50% of the survey objects have L_bol >10^12L_sun, in the quasar regime. We present composite spectra for type-2 quasars and for objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared - emission-line luminosity correlation and present the results of cross-correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) there exist mid-infrared selected AGN candidates which lack AGN signatures in their optical spectra, but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGN often differ.
Luminous Infrared (IR) Galaxies (LIRGs) are an important cosmological class of galaxies as they are the main contributors to the co-moving star formation rate density of the universe at z=1. In this paper we present a GTO Spitzer IRS program aimed to obtain spectral mapping of a sample of 14 local (d<76Mpc) LIRGs. The data cubes map, at least, the central 20arcsec x 20arcsec to 30arcsec x 30arcsec regions of the galaxies, and use all four IRS modules covering the full 5-38micron spectral range. The final goal of this project is to characterize fully the mid-IR properties of local LIRGs as a first step to understanding their more distant counterparts. In this paper we present the first results of this GTO program. The IRS spectral mapping data allow us to build spectral maps of the bright mid-IR emission lines (e.g., [NeII], [NeIII], [SIII], H_2), continuum, the 6.2 and 11.3micron PAH features, and the 9.7micron silicate feature, as well as to extract 1D spectra for regions of interest in each galaxy. The IRS data are used to obtain spatially resolved measurements of the extinction using the 9.7micron silicate feature, and to trace star forming regions using the neon lines and the PAH features. We also investigate a number of AGN indicators, including the presence of high excitation emission lines and a strong dust continuum emission at around 6micron. We finally use the integrated Spitzer/IRS spectra as templates of local LIRGs. We discuss several possible uses for these templates, including the calibration of the star formation rate of IR-bright galaxies at high redshift. We also predict the intensities of the brightest mid-IR emission lines for LIRGs as a function of redshift, and compare them with the expected sensitivities of future space IR missions.
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