Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMid-Infrared Variability from the Spitzer Deep, Wide-Field Survey
134
0
0.0
(
0
)
Authors
Szymon Kozlowski
Ask ChatGPT about the research
No Arabic abstract
We use the multi-epoch, mid-infrared Spitzer Deep, Wide-Field Survey to investigate the variability of 474,179 objects in 8.1 deg^2 of the NDWFS Bootes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 micron bands. We find that 1.1% of the studied sample meet our standard selection criteria for being classed as a variable source. We require that the 3.6 and 4.5 micron light-curves are strongly correlated (r>0.8) and that their joint variance exceeds that for all sources with the same magnitude by 2 sigma. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBootes survey, radio catalogs, 24 micron-selected AGN candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects. Most of the stellar, galaxy and unclassified sources are false positives. For our standard selection criteria, 11-12% of the mid-IR counterparts to X-ray sources, 24 micron-selected AGN candidates and spectroscopically identified AGNs show variability. Mid-IR AGN variability can be well described by a single power-law structure function with a power-law index of 0.5 at both 3.6 and 4.5 microns, and an amplitude of 0.1 mag on rest-frame time scales of 2 years. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities. (Abridged)
rate research
Read More
The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of ten square degrees in the Bootes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Cycle four Spitzer Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit -- for the first time -- the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z~3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS datasets will thus be especially useful for characterizing galaxy evolution beyond z~1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly-released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 x 10e5 distinct sources detected to the average 5-sigma, 4 diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 micron, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 min integration time of the SDWFS IRAC imaging, more than 50% of isolated FIRST radio sources and more than 80% of on-axis XBootes sources are detected out to 8.0 micron. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.
We discuss the clustering properties of galaxies with signs of ongoing star formation detected by the Spitzer Space Telescope at 24mum band in the SWIRE Lockman Hole field. The sample of mid-IR-selected galaxies includes ~20,000 objects detected above a flux threshold of S24mum=310muJy. We adopt optical/near-IR color selection criteria to split the sample into the lower-redshift and higher-redshift galaxy populations. We measure the angular correlation function on scales of theta=0.01-3.5 deg, from which, using the Limber inversion along with the redshift distribution established for similarly selected source populations in the GOODS fields (Rodighiero et al. 2010), we obtain comoving correlation lengths of r0=4.98+-0.28 h^-1 Mpc and r0 =8.04+-0.69 h^-1 Mpc for the low-z (<z>=0.7) and high-z (<z>=1.7) subsamples, respectively. Comparing these measurements with the correlation functions of dark matter halos identified in the Bolshoi cosmological simulation (Klypin et al. 2011}, we find that the high-redshift objects reside in progressively more massive halos reaching Mtot>3e12 h^-1 Msun, compared to Mtot>7e11 h^-1 Msun for the low-redshift population. Approximate estimates of the IR luminosities based on the catalogs of 24mum sources in the GOODS fields show that our high-z subsample represents a population of distant ULIRGs with LIR>10^12Lsun, while the low-z subsample mainly consists of LIRGs, LIR~10^11Lsun. The comparison of number density of the 24mum selected galaxies and of dark matter halos with derived minimum mass Mtot shows that only 20% of such halos may host star-forming galaxies.
We present new observational determination of the evolution of the rest-frame 70 and 160 micron and total infrared (TIR) galaxy luminosity functions (LFs) using 70 micron data from the Spitzer Wide-area Infrared Extragalactic Legacy Survey (SWIRE). The LFs were constructed for sources with spectroscopic redshifts only in the XMM-LSS and Lockman Hole fields from the SWIRE photometric redshift catalogue. The 70 micron and TIR LFs were constructed in the redshift range 0<z<1.2 and the 160 micron LF was constructed in the redshift range 0<z<0.5 using a parametric Bayesian and the vmax methods. We assume in our models, that the faint-end power-law index of the LF does not evolve with redshifts. We find the the double power-law model is a better representation of the IR LF than the more commonly used power-law and Gaussian model. We model the evolution of the FIR LFs as a function of redshift where where the characteristic luminosity, $L^ast$ evolve as $propto(1+z)^{alpha_textsc{l}}$. The rest-frame 70 micron LF shows a strong luminosity evolution out to z=1.2 with alpha_l=3.41^{+0.18}_{-0.25}. The rest-frame 160 micron LF also showed rapid luminosity evolution with alpha_l=5.53^{+0.28}_{-0.23} out to z=0.5. The rate of evolution in luminosity is consistent with values estimated from previous studies using data from IRAS, ISO and Spitzer. The TIR LF evolves in luminosity with alpha_l=3.82^{+0.28}_{-0.16} which is in agreement with previous results from Spitzer 24 micron which find strong luminosity evolution. By integrating the LF we calculated the co-moving IR luminosity density out to z=1.2, which confirm the rapid evolution in number density of LIRGs and ULIRGs which contribute ~68^{+10}_{-07} % to the co-moving star formation rate density at z=1.2. Our results based on 70 micron data confirms that the bulk of the star formation at z=1 takes place in dust obscured objects.
We present a new catalogue of mid-IR sources using the AKARI NEP-Deep survey. The InfraRed Camera (IRC) onboard AKARI has a comprehensive mid-IR wavelength coverage with 9 photometric bands at 2 - 24 micron. We utilized all of these bands to cover a nearly circular area adjacent to the North Ecliptic Pole (NEP). We designed the catalogue to include most of sources detected in 7, 9, 11, 15 and 18 micron bands, and found 7284 sources in a 0.67 deg^2 area. From our simulations, we estimate that the catalogue is ~80 per cent complete to 200 micro Jy at 15 - 18 micron, and ~10 per cent of sources are missed, owing to source blending. Star-galaxy separation is conducted using only AKARI photometry, as a result of which 10 per cent of catalogued sources are found to be stars. The number counts at 11, 15, 18, and 24 micron are presented for both stars and galaxies. A drastic increase in the source density is found in between 11 and 15 micron at the flux level of ~300 micro Jy. This is likely due to the redshifted PAH emission at 8 micron, given our rough estimate of redshifts from an AKARI colour-colour plot. Along with the mid-IR source catalogue, we present optical-NIR photometry for sources falling inside a Subaru/Sprime-cam image covering part of the AKARI NEP-Deep field, which is deep enough to detect most of AKARI mid-IR sources, and useful to study optical characteristics of a complete mid-IR source sample.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
