A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2

By A. Dey, B. Soifer, Vandana Desai, K. Brand, É. Le Floc'h, Michael J. I. Brown, B. Jannuzi, Lee Armus, S. Bussmann, M. Brodwin and 5 more. 2008

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The Spitzer Space Telescope has revealed a significant population of high-redshift (z ∼ 2) dust-obscured galaxies with large mid-infrared to ultraviolet luminosity ratios. Due to their optical faintness, these galaxies have been previously missed in traditional optical studies of the distant universe. We present a simple method for selecting this high-redshift population based solely on the ratio of the observed mid-infrared 24 μm to optical R-band flux density. We apply this method to observations of the ≈8.6 deg2 NOAO Deep Wide-Field Survey Boötes field, and uncover ≈2600 dust-obscured galaxy candidates [i.e., 0.089 arcmin−2) with 24 μm flux densities F24 μ m ⩾ 0.3 mJy and (R − [ 24]) ⩾ 14 (i.e., Fν(24 μ m)/Fν(R) ≳ 1000]. These galaxies have no counterparts in the local universe. They represent 7% ± 0.6% of the 24 μm source population at F24 μ m ⩾ 1 mJy but increase to ≈13% ± 1% of the population at ≈0.3 mJy. These galaxies exhibit evidence of both star formation and AGN activity, with the brighter 24 μm sources being more AGN-dominated. We have measured spectroscopic redshifts for 86 of these galaxies, and find a broad redshift distribution centered at . The space density of this population is ΣDOG(F24μ m ⩾ 0.3 mJy) = (2.82 ± 0.05) × 10−5h370 Mpc −3, similar to that of bright submillimeter-selected galaxies at comparable redshifts. These redshifts imply large luminosities, with median ν Lν(8 μ m) ≈ 4 × 1011 L☉. The infrared luminosity density contributed by this relatively rare dust-obscured galaxy population is log (IRLD) ≈ 8.23+ 0.18−0.30. This is ≈60+ 40−15% of that contributed by z ∼ 2 ultraluminous infrared galaxies (ULIRGs, with LIR > 1012 L☉); our simple selection thus identifies a significant fraction of z ∼ 2 ULIRGs. This IRLD is ≈26% ± 14% of the total contributed by all z ∼ 2 galaxies. We suggest that these dust-obscured galaxies are the progenitors of luminous (~4L*) present-day galaxies, seen undergoing an extremely luminous, short-lived phase of both bulge and black hole growth. They may represent a brief evolutionary phase between submillimeter-selected galaxies and less obscured quasars or galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1ef6fe209779577bb781dc8c3d9920ad3d7a4278

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A STEEP FAINT-END SLOPE OF THE UV LUMINOSITY FUNCTION AT z ∼ 2–3: IMPLICATIONS FOR THE GLOBAL STELLAR MASS DENSITY AND STAR FORMATION IN LOW-MASS HALOS (2008, background): “Similarly, 24µm-bright galaxies (f24µm ≥ 0.3 mJy) with red optical to mid-IR colors (R − [24] ≥ 14) have a space density in the redshift range 0.5 ≤ z ≤ 3.5 of (2.82 ± 0.05) × 10−5 Mpc−3 (Dey et al. 2008), almost all of which lie below L∗, the characteristic unobscured UV luminosity.”
MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. I. CHARACTERIZING WISE-SELECTED ACTIVE GALACTIC NUCLEI IN COSMOS (2012, unknown): “…2004, 2007; Stern et al. 2005; Alonso-Herrero et al. 2006; Barmby et al. 2006; Mart́ınez-Sansigre et al. 2006, 2007; Donley et al. 2007, 2008, 2012; Dey et al. 2008; Fiore et al. 2008, 2009; Hatziminaoglou et al. 2008; Rigopoulou et al. 2009; Seymour et al. 2007; De Breuck et al. 2010; Eckart et…”
CHASING HIGHLY OBSCURED QSOs IN THE COSMOS FIELD (2008, background): “Dey et al. (2008) obtained optical spectroscopy of a rather large sample of objects with extreme F(24µm)/F(R) flux ratios and F(24µ) > 0.3mJy.”
Enhanced star formation rates in AGN hosts with respect to inactive galaxies from PEP-Herschel observations (2012, unknown): “2005; Sajina et al. 2008; Dey et al. 2008; Donley et al. 2010; Georgakakis et al. 2010).”
Star formation and mass assembly in high-redshift galaxies (2009, background): “Following a different approach, Fiore et al. (2008) identified a population of highly obscured AGNs candidates in the entireKs–selected sample, selected on the basis of their very red spectrum (F24µm/F(R) > 1000 and R−Ks > 4.5) (see also Dey et al. 2008).”
Deep Spitzer 24 μm COSMOS Imaging. I. The Evolution of Luminous Dusty Galaxies—Confronting the Models (2009, background): “…have played a key role in driving the coeval growth of bulges and super-massive black holes but whose contribution is usually underestimated by surveys performed at other wavelengths (e.g., Houck et al. 2005; Polletta et al. 2006; Alonso-Herrero et al. 2006; Dey et al. 2008; Fiore et al. 2008).”
HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD (2009, result): “We find that the range of SEDs seen among those categorized as “background galaxies” and “probable galaxies” is similar to those seen in other samples of distant galaxies observed by Spitzer (e.g., Dey et al. 2008; Kozłowski & Kochanek 2009).”
GOODS-HERSCHEL AND CANDELS: THE MORPHOLOGIES OF ULTRALUMINOUS INFRARED GALAXIES AT z ∼ 2 (2011, background): “Another selection of ULIRGs that has been studied at high redshift in the literature are the color selected Dust Obscured Galaxies (DOGs: fν(24µm)/fν(R) ≥ 1000), Dey et al. 2008).”
Dusty Star Forming Galaxies at High Redshift (2014, background): “The population of Dust Obscured Galaxies (DOGs; Dey et al., 2008; Pope et al., 2008a) define the population of 24 µm-selected galaxies that have extremely red colors (i.e. (R-[24]) ≥ 14 mags [Vega]).”
Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “At higher redshifts (z ∼ 1–3), galaxies with the luminosities of LIRGs and ULIRGs may be more ‘normal’ galaxies, in the sense that they are relatively undisturbed discs rather than mergers (Sajina et al. 2007; Yan et al. 2007; Dasyra et al. 2008; Dey et al. 2008; Melbourne et al. 2008).”
CHARACTERIZING THE MID-INFRARED EXTRAGALACTIC SKY WITH WISE AND SDSS (2012, methodology): “For example, red 24µm to r-band colors (r − [24] > 14; Vega) have been used in the Extragalactic First Look Survey (XFLS; (Yan et al. 2004)) and Boötes field to successfully select many highly obscured galaxies at z ∼ 2 (Yan et al. 2005, 2007; Dey et al. 2008).”
Active galactic nuclei: what’s in a name? (2017, methodology): “For example, using the colour between the optical R-band and the MIPS 24 µm band, Dey et al. (2008) found a new class of objects, dubbed Dust-Obscured Galaxies or DOGs, many of which host heavily reddened AGN (see e.g. Melbourne et al. 2012).”
x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared (2020, background): “14), the results below might not be applicable to some particular sources, for which the observed MIR emission is dominated by AGNs (e.g. hot dust-obscured galaxies, hot DOGs; Dey et al. 2008; Vito et al. 2018).”
THE ERA OF STAR FORMATION IN GALAXY CLUSTERS (2013, result): “This model also corroborates the findings of Brodwin et al. (2008) that the brightest Dust-Obscured Galaxies (DOGS, Dey et al. 2008; Pope et al. 2008), which are dusty AGN-dominated ULIRGs at 1.5 . z .”
THE XMM-NEWTON WIDE-FIELD SURVEY IN THE COSMOS FIELD (XMM-COSMOS): DEMOGRAPHY AND MULTIWAVELENGTH PROPERTIES OF OBSCURED AND UNOBSCURED LUMINOUS ACTIVE GALACTIC NUCLEI (2010, background): “In particular, the combination of observed-frame mid-infrared, near infrared and X–ray to optical flux ratios has been exploited recently in the literature to isolate obscured AGN (see, e.g., F03, Martinez-Sansigre et al. 2005, 2006, Fiore et al. 2008, Donley et al. 2008, Dey et al. 2008).”