We reinvestigate the relationship between the characteristic broad-line region size (R sub(BLR)) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of ...the best available determinations of R sub(BLR) for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of R sub(BLR) for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation R sub(BLR) 8 L super(a), we find that the mean best-fitting a is about 0.67 c 0.05 for the optical continuum and the broad Hb luminosity, about 0.56 c 0.05 for the UV continuum luminosity, and about 0.70 c 0.14 for the X-ray luminosity. We also find an intrinsic scatter of 640% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.
ABSTRACT We present a detailed, multi-wavelength study of star formation (SF) and active galactic nucleus (AGN) activity in 11 near-infrared (IR) selected, spectroscopically confirmed massive ( 1014 ...M ) galaxy clusters at 1 < z < 1.75. Using new deep Herschel/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGNs through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs) and specific SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at z 1.4 is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores (r < 0.5 Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by z ∼ 1. Enhanced SFRs are found in lower mass ( ) cluster galaxies. We find significant variation in SF from cluster to cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGNs in clusters from z = 0.5-2, finding an excess AGN fraction at z 1, suggesting environmental triggering of AGNs during this epoch. We argue that our results-a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGNs-are consistent with a co-evolution between SF and AGNs in clusters and an increased merger rate in massive halos at high redshift.
We present a detailed census of galaxies in and around PC 217.96+32.3, a spectroscopically confirmed Coma analog at z = 3.78. Diverse galaxy types identified in the field include Ly emitters (LAEs), ...massive star-forming galaxies, and ultramassive galaxies ( ) which may have already halted their star formation. The sky distribution of the star-forming galaxies suggests the presence of a significant overdensity (δSFG 8 2), which is spatially offset from the previously confirmed members by 3-4 Mpc to the west. Candidate quiescent and post-starburst galaxies are also found in large excess (a factor of ∼8-15 higher surface density than the field's), although their redshifts are less certain. We estimate that the total enclosed mass traced by the candidate star-forming galaxies is roughly comparable to that of PC 217.96+32.3 traced by the LAEs. We speculate that the true extent of PC 217.96+32.3 may be larger than previously known, half of which is missed by our LAE selection. Alternatively, the newly discovered overdensity may belong to another Coma progenitor not associated with PC 217.96+32.3. Expectations from theory suggest that both scenarios are equally unlikely (<1%) in the cosmic volume probed in our survey. If confirmed as a single structure, its total mass will be well in excess of Coma's, making it an exceptionally large cosmic structure rarely seen even in large cosmological simulations. Finally, we find that the protocluster galaxies follow the same star formation rate-M* scaling relation as the field galaxies, suggesting that the environmental effect at z ∼ 4 is a subtle one at best for normal star-forming galaxies.
Abstract
We report the detection of diffuse Ly
α
emission, or Ly
α
halos (LAHs), around star-forming galaxies at
z
≈ 3.78 and 2.66 in the NOAO Deep Wide-Field Survey Boötes field. Our samples ...consist of a total of ∼1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Ly
α
images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Ly
α
radial profile into a compact galaxy-like and an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Ly
α
luminosities, but not on Ly
α
equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Ly
α
emitters (
M
UV
≳ −21), exhibit LAH sizes of 5–6 kpc. However, the most UV- or Ly
α-
luminous galaxies have more extended halos with scale-lengths of 7–9 kpc. The stacked Ly
α
radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. However, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, H
i
column density, and outflow velocity) change with halo mass and/or star formation rates.
We present an updated determination of the z ~ 4 QSO luminosity function (QLF), improving the quality of the determination of the faint end of the QLF presented by Glikman et al. (2010). We have ...observed an additional 43 candidates from our survey sample, yielding one additional QSO at z = 4.23 and increasing the completeness of our spectroscopic follow-up to 48% for candidates brighter than R = 24 over our survey area of 3.76 deg2. We study the effect of using K-corrections to compute the rest-frame absolute magnitude at 1450 A compared with measuring M 1450 directly from the object spectra. We find a luminosity-dependent bias: template-based K-corrections overestimate the luminosity of low-luminosity QSOs, likely due to their reliance on templates derived from higher luminosity QSOs. Combining our sample with bright quasars from the Sloan Digital Sky Survey and using spectrum-based M 1450 for all the quasars, we fit a double power law to the binned QLF. Our best fit has a bright-end slope, Delta *a = 3.3 ? 0.2, and faint-end slope, Delta *b = 1.6+0.8 --0.6. Our new data revise the faint-end slope of the QLF down to flatter values similar to those measured at z ~ 3. The break luminosity, though poorly constrained, is at M* = --24.1+0.7 --1.9, approximately 1-1.5 mag fainter than at z ~ 3. This QLF implies that QSOs account for about half the radiation needed to ionize the intergalactic medium at these redshifts.
Mid-infrared photometry provides a robust technique for identifying active galaxies. While the ultraviolet to mid-infrared (l < 5 km) continuum of stellar populations is dominated by the composite ...blackbody curve and peaks at approximately 1.6 km, the ultraviolet to mid-infrared continuum of active galactic nuclei (AGNs) is dominated by a power law. Consequently, with a sufficient wavelength baseline, one can easily distinguish AGNs from stellar populations. Mirroring the tendency of AGNs to be bluer than galaxies in the ultraviolet, where galaxies (and stars) sample the blue, rising portion of stellar spectra, AGNs tend to be redder than galaxies in the mid-infrared, where galaxies sample the red, falling portion of the stellar spectra. We report on Spitzer Space Telescope mid-infrared colors, derived from the IRAC Shallow Survey, of nearly 10,000 spectroscopically identified sources from the AGN and Galaxy Evolution Survey. On the basis of this spectroscopic sample, we find that simple mid-infrared color criteria provide remarkably robust separation of active galaxies from normal galaxies and Galactic stars, with over 80% completeness and less than 20% contamination. Considering only broad-lined AGNs, these mid-infrared color criteria identify over 90% of spectroscopically identified quasars and Seyfert 1 galaxies. Applying these color criteria to the full imaging data set, we discuss the implied surface density of AGNs and find evidence for a large population of optically obscured active galaxies.
ABSTRACT We present new observations of the field containing the z = 3.786 protocluster PC 217.96+32.3. We confirm that it is one of the largest known and most overdense high-redshift structures. ...Such structures are rare even in the largest cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image a 1 2 × 0 6 area ( 150 × 75 comoving Mpc) surrounding the protocluster's core and discovered 165 candidate Ly emitting galaxies (LAEs) and 788 candidate Lyman Break galaxies (LBGs). There are at least two overdense regions traced by the LAEs, the largest of which shows an areal overdensity in its core (i.e., within a radius of 2.5 comoving Mpc) of 14 7 relative to the average LAE spatial density ( ) in the imaged field. Further, is twice that derived by other field LAE surveys. Spectroscopy with Keck/DEIMOS yielded redshifts for 164 galaxies (79 LAEs and 85 LBGs); 65 lie at a redshift of 3.785 0.010. The velocity dispersion of galaxies near the core is = 350 40 km s−1, a value robust to selection effects. The overdensities are likely to collapse into systems with present-day masses of >1015 M and >6 × 1014 M . The low velocity dispersion may suggest a dynamically young protocluster. We find a weak trend between narrow-band (Ly ) luminosity and environmental density: the Ly luminosity is enhanced on average by 1.35× within the protocluster core. There is no evidence that the Ly equivalent width depends on environment. These suggest that star formation and/or active galactic nucleus (AGN) activity is enhanced in the higher-density regions of the structure. PC 217.96+32.3 is a Coma cluster analog, witnessed in the process of formation.
We have traced the past 7 Gyr of red galaxy stellar mass growth within dark matter halos. We have determined the halo occupation distribution, which describes how galaxies reside within dark matter ...halos, using the observed luminosity function and clustering of 40,696 image red galaxies in Booetes. Half of image10 super(11.9) h super(-1) M sub(image) halos host a red central galaxy, and this fraction increases with increasing halo mass. We do not observe any evolution of the relationship between red galaxy stellar mass and host halo mass, although we expect both galaxy stellar masses and halo masses to evolve over cosmic time. We find that the stellar mass contained within the red population has doubled since image, with the stellar mass within red satellite galaxies tripling over this redshift range. In cluster mass halos (>10 super(14) h super(-1) M sub(image)) most of the stellar mass resides within satellite galaxies and the intracluster light, with a minority of the stellar mass residing within central galaxies. The stellar masses of the most luminous red central galaxies are proportional to halo mass to the power of image0.35. We thus conclude that halo mergers do not always lead to rapid growth of central galaxies. While very massive halos often double in mass over the past 7 Gyr, the stellar masses of their central galaxies typically grow by only image30%.
The spectroscopic discovery of five galaxies at z = 3.783 + or - 0.002 lying within 1 Mpc of one another led us to undertake a deep narrow- and broadband imaging survey of the surrounding field. The ...galaxy distribution within the field is highly non-uniform, exhibiting three large ( approximately 3-5x) overdensities separated by 8-14 Mpc (physical) and possibly connected by filamentary structures traced by LAEs. The observed number of LAEs in the entire field is nearly twice the average expected in field environments based on estimates of the Ly alpha luminosity function at these redshifts. The highest concentration of galaxies is located at the southern end of the image, suggesting that the current imaging may not map the true extent of the large-scale structure. Finding three large protocluster candidates within a single 0.3 deg super(2) field is highly unusual; expectations from theory suggest that such alignments should occur less than 2% of the time.
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