We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly alpha -emitting (LAE) galaxies at z unk 3.1 discovered in deep narrowband MUSYC ...imaging of the Extended Chandra Deep Field-South. LAEs were selected to have observed frame equivalent widths >80 AAA and emission line fluxes >1.5 x 10 super(-17) ergs cm super(-2) s super(-1). Only 1% of our LAE sample appears to host AGNs. The LAEs exhibit a moderate spatial correlation length of unk = unk Mpc, corresponding to a bias factor b = unk, which implies median dark matter halo masses of log sub(10)M unk = unk M unk. Comparing the number density of LAEs, 1.5 plus or minus 0.3 x 10 super(-3) Mpc super(-3), with the number density of these halos finds a mean halo occupation similar to 1%-10%. The evolution of galaxy bias with redshift implies that most z = 3.1 LAEs evolve into present-day galaxies with unk, whereas other z > 3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z = 0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of unk. Only 30% of LAEs have sufficient stellar mass (> similar to 3 x unk M unk) to yield detections in deep Spitzer IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+3.6, 4.5, 5.6, 8.0 mu m fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass ( unk x unk M unk), moderate star formation rate (2 plus or minus 1 M unk yr super(-1)), a young component age of unk Myr, and little dust (Av < 0.2). The best-fit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.
THE EXTENDED OPTICAL DISK OF M101 Mihos, J Christopher; Harding, Paul; Spengler, Chelsea E ...
Astrophysical journal/The Astrophysical journal,
01/2013, Letnik:
762, Številka:
2
Journal Article
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We have used deep, wide-field optical imaging to study the faint outskirts of the luminous spiral galaxy M101 (NGC 5457) as well as its surrounding environment. Over 6 deg super(2), our imaging has a ...limiting surface brightness of mu sub(B) ~ 29.5 mag arcsec super(-2), and has revealed the stellar structure of M101's disk out to nearly 25' (50 kpc), 3 times our measured R sub(25) isophotal size of the optical disk. We also detect another, redder spur of extended light to the east of the disk, and both structures are reminiscent of features produced during fly-by galaxy interactions. We consider the properties of M101's outer disk in light of possible past interactions with the nearby companion galaxies NGC 5477 and NGC 5474. Our data suggest an ongoing buildup of M101's outer disk due to encounters in the group environment triggering extended star formation and tidal heating of existing disk populations.
We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our ...data trace M49's stellar halo out to ~100 kpc (7r sub(e)), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B ? V ~ 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with Fe/H < ?1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.
We present a Bayesian approach to the redshift classification of emission-line galaxies when only a single emission line is detected spectroscopically. We consider the case of surveys for ...high-redshift Ly -emitting galaxies (LAEs), which have traditionally been classified via an inferred rest-frame equivalent width (EW; ) greater than 20 Å. Our Bayesian method relies on known prior probabilities in measured emission-line luminosity functions and EW distributions for the galaxy populations, and returns the probability that an object in question is an LAE given the characteristics observed. This approach will be directly relevant for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), which seeks to classify ∼106 emission-line galaxies into LAEs and low-redshift emitters. For a simulated HETDEX catalog with realistic measurement noise, our Bayesian method recovers 86% of LAEs missed by the traditional > 20 Å cutoff over 2 < z < 3, outperforming the EW cut in both contamination and incompleteness. This is due to the method's ability to trade off between the two types of binary classification error by adjusting the stringency of the probability requirement for classifying an observed object as an LAE. In our simulations of HETDEX, this method reduces the uncertainty in cosmological distance measurements by 14% with respect to the EW cut, equivalent to recovering 29% more cosmological information. Rather than using binary object labels, this method enables the use of classification probabilities in large-scale structure analyses. It can be applied to narrowband emission-line surveys as well as upcoming large spectroscopic surveys including Euclid and WFIRST.
We report the search for intracluster light in four Abell type II-III (non- cD) galaxy clusters: A801, A1234, A1553, and A1914. We find that on average these clusters contain approx10% of their ...detected stellar luminosity in a diffuse component. We show that for two of the clusters the intracluster light closely follows the galaxy distribution, but in the other two cases, there are noticeable differences between the spatial distribution of the galaxies and the intracluster light. We report the results of a search for intracluster tidal debris in each cluster and note that A1914 in particular has a number of strong tidal features likely due to its status as a recent cluster merger. One of the A1914 features appears to be spatially coincident with an extension seen in weak lensing maps, implying that the feature traces a large amount of mass. We compare these results with numerical simulations of hierarchically formed galaxy clusters and find good general agreement between the observed and simulated images, although we also find that our observations sample only the brightest features of the intracluster light. Together, these results suggest that intracluster light can be a valuable tool in determining the evolutionary state of galaxy clusters.
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