Recent galaxy evolution models suggest that feedback from active galactic nuclei (AGNs) may be responsible for suppressing star formation in their host galaxies and the subsequent migration of these ...systems onto the red sequence. To investigate the role of AGNs in driving the evolution of their hosts, we have carried out a study of the environments and optical properties of galaxies harboring X-ray luminous AGNs in the Cl1604 supercluster at z {approx} 0.9. Making use of Chandra, HST/ACS and Keck/DEIMOS observations, we examine the integrated colors, morphologies, and spectral properties of nine moderate-luminosity (L {sub X} {approx} 10{sup 43} erg s{sup -1}) type 2 Seyferts detected in the Cl1604 complex. We find that the AGNs are predominantly hosted by luminous spheroids and/or bulge-dominated galaxies which have colors that place them in the valley between the blue cloud and red sequence in color-magnitude space, consistent with predictions that AGN hosts should constitute a transition population. Half of the hosts have bluer overall colors as a result of blue resolved cores in otherwise red spheroids and a majority show signs of recent or pending interactions. We also find a substantial number exhibit strong Balmer absorption features indicative of post-starburst galaxies, despite the fact that we detect narrow O II emission lines in all of the host spectra. If the O II lines are due in part to AGN emission, as we suspect, then this result implies that a significant fraction of these galaxies (44%) have experienced an enhanced level of star formation within the last {approx}1 Gyr which was rapidly suppressed. Furthermore we observe that the hosts galaxies tend to avoid the densest regions of the supercluster and are instead located in intermediate density environments, such as the infall region of a massive cluster or in poorer systems undergoing assembly. Overall we find that the properties of the nine host galaxies are generally consistent with a scenario in which recent interactions have triggered both increased levels of nuclear activity and an enhancement of centrally concentrated star formation, followed by a rapid truncation of the latter, possibly as a result of feedback from the AGN itself. Our finding that the hosts of moderate-luminosity AGNs within the Cl1604 supercluster are predominantly a transition population suggests that AGN feedback may play an important role in accelerating galaxy evolution in large-scale structures.
We present a study on stellar properties of Lyman-alpha (Ly$\alpha$) emitters
at 5 $< z <$ 8.2. We use 247 photometrically-selected, lensed, high-redshift,
low luminosity galaxy candidates with ...spectroscopic follow-up. Of these, 38 are
confirmed spectroscopically to be between 5 $< z <$ 8.2 via detection of
Ly$\alpha$. For each galaxy and candidate, we estimate stellar mass, star
formation rate, specific star formation rate, and mass-weighted age with
spectral energy distribution fitting. We also measure the UV $\beta$ slope and
luminosity using values from photometry. We find no strong correlation between
Ly$\alpha$ equivalent width and any of these properties, as well as no
significant difference between the physical properties of Ly$\alpha$ emitters
and candidates without Ly$\alpha$ detected. This lack of expected trends may be
explained by a combination of the evolving opacity of the IGM at these
redshifts as well as the unique phase space probed by our lensed sample. Via
tests on other galaxy samples which show varying strengths of correlations, we
conclude that if there exist any relationships between Ly$\alpha$ EW and
physical properties in the underlying population of faint galaxies, they are
weak correlations. We also present the results of a spectroscopic search for
CIII emission in confirmed Ly$\alpha$ emitters at $z \sim 7$, finding no CIII
detections, but putting constraints on strong AGN activity and extreme nebular
emission.
We present the first results of a search for Lya emitters (LAEs) in the DEEP2 spectroscopic database that uses a search technique that is different from but complementary to traditional narrowband ...imaging surveys. We have visually inspected image20% of the available DEEP2 spectroscopic data and have found nine high-quality LAEs with clearly asymmetric line profiles and an additional 10 objects of lower quality, some of which may also be LAEs. Our survey is most sensitive to LAEs at image and that is indeed where all but one of our high-quality objects are found. We find the number density of our spectroscopically discovered LAEs to be consistent with those found in narrowband imaging searches. The combined, averaged spectrum of our nine high-quality objects is well fit by a two-component model, with a second, lower amplitude component redshifted by image420 km s(-1) with respect to the primary Lya line, consistent with large-scale outflows from these objects. We conclude by discussing the advantages and future prospects of blank-sky spectroscopic surveys for high-z LAEs.
We report on a \(\rm{CII}_{158\mu\rm{m}}\) search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed {\lya} emitting galaxies at \(z \sim 7\). Our targets are ...ultra-violet (UV) faint systems with stellar masses on the order of \(M_{*} \sim 10^{9} M_{\odot}\). We detect a single CII line emission (\(4\sigma\)) from the brightest (\(L \sim 2.4 \times 10^{10}L_{\odot}\)) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (\(z_{\rm{CII}} = 6.3151 \pm 0.0005\)) for MACS0454-1251 and measure a {\lya} velocity offset of \(\Delta v \approx 300 \pm 70 \rm{km\,s}^{-1}\). The remaining two galaxies we detect no {\ct} but provide \(3 \sigma\) upper limits on their {\ct} line luminosities which we use to investigate the \(L_{\textrm{CII}} - \rm{SFR}\) relation. Overall our single {\ct} detection shows agreement with the relation for dwarf and local starburst galaxies. Our CII deficient galaxies could potentially be exhibiting low metallicities (\(Z<Z_{\odot}\)). Another possible explanation for weaker CII emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of \(T_{d}=35 \rm{K}\) dust masses (\(M_{\rm{dust}}\)) range from \(< 4.8 \times 10^{7} M_{\odot} \) to \(2.3 \times 10^{8} M_{\odot}\). Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing CII emission.
The connection between galaxies and dark matter halos is often quantified
using the stellar mass-halo mass (SMHM) relation. Optical and near-infrared
imaging surveys have led to a broadly consistent ...picture of the evolving SMHM
relation based on measurements of galaxy abundances and angular correlation
functions. Spectroscopic surveys at $z \gtrsim 2$ can also constrain the SMHM
relation via the galaxy autocorrelation function and through the
cross-correlation between galaxies and Ly$\alpha$ absorption measured in
transverse sightlines; however, such studies are very few and have produced
some unexpected or inconclusive results. We use $\sim$3000 spectra of
$z\sim2.5$ galaxies from the Lyman-alpha Tomography IMACS Survey (LATIS) to
measure the galaxy-galaxy and galaxy-Ly$\alpha$ correlation functions in four
bins of stellar mass spanning $10^{9.2} \lesssim M_* / M_{\odot} \lesssim
10^{10.5}$. Parallel analyses of the MultiDark N-body and ASTRID hydrodynamic
cosmological simulations allow us to model the correlation functions, estimate
covariance matrices, and infer halo masses. We find that results of the two
methods are mutually consistent and are broadly in accord with standard SMHM
relations. This consistency demonstrates that we are able to accurately measure
and model Ly$\alpha$ transmission fluctuations $\delta_F$ in LATIS. We also
show that the galaxy-Ly$\alpha$ cross-correlation, a free byproduct of optical
spectroscopic galaxy surveys at these redshifts, can constrain halo masses with
similar precision to galaxy-galaxy clustering.
Recent James Webb Space Telescope (JWST) observations have revealed a
surprisingly abundant population of faint, dusty active galactic nuclei (AGNs)
at z~4-7. Together with the presence of ...supermassive black holes (SMBHs) at
z>6, this raises questions about the formation and growth histories of early
black holes. Current theories for the formation of seed black holes from the
death of the first stars (i.e. light seeds) and/or the direct collapse of
primordial gas clouds (i.e. heavy seeds) still lack observational confirmation.
Here, we present LID-568, a low-mass (7.2e6Msun) black hole hosting powerful
outflows that is observed in an extreme phase of rapid growth at z~4. This
object is similar to other JWST-discovered faint AGN populations, but is bright
in X-ray emission and accreting at more than 4000% of the limit at which
radiation pressure exceeds the force of gravitational attraction of the black
hole (i.e. super-Eddington accretion). Analysis of JWST NIRSpec/IFU data
reveals spatially extended Ha emission with velocities of ~ -600 - -500 km/s
relative to the central black hole, indicative of robust nuclear-driven
outflows. LID-568 represents an elusive low-mass black hole experiencing
super-Eddington accretion as invoked by models of early black hole formation.
This discovery showcases a previously undiscovered key parameter space and
offers crucial insights into rapid black hole growth mechanisms in the early
universe.
We present an analysis of the number density of galaxies as a function of stellar mass (i.e., the stellar mass function, SMF) in the COSMOS field at z~3.3, making a comparison between the SMF in ...overdense environments and the SMF in the coeval field. In particular, this region contains the Elentári proto-supercluster, a system of 6 extended overdensities spanning ~70 cMpc on a side. A clear difference is seen in the high-mass slope of these SMFs, with overdense regions showing an increase in the ratio of high-mass galaxies to low-mass galaxies relative to the field, indicating a more rapid build-up of stellar mass in overdense environments. This result qualitatively agrees with analyses of clusters at z~1, though the differences between protocluster and field SMFs at z~3.3 are smaller. While this is consistent with overdensities enhancing the evolution of their member galaxies, potentially through increased merger rates, whether this enhancement begins in protocluster environments or even earlier in group environments is still unclear. Though the measured fractions of quiescent galaxies between the field and overdense environments do not vary significantly, implying that this stellar mass enhancement is ongoing and any starbursts triggered by merger activity have not yet quenched, we note that spectroscopic observations are biased towards star-forming populations, particularly for low-mass galaxies. If mergers are indeed responsible, high resolution imaging of Elentári and similar structures at these early epochs should then reveal increased merger rates relative to the field. Larger samples of well-characterized overdensities are necessary to draw broader conclusions in these areas.
We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), \(x_{\textrm{HI}}\), at \(z \sim\) 6-8 using the properties of Lyman break galaxies during the ...Epoch of Reionization. We use large samples of LBG candidates at \(5.5 \leq z \leq 8.2\) with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-\(\alpha\) equivalent width (EW) for detections or the EW limit spectrum for nondetections to parameterize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at \(z\) \(\sim\) 6.0, we are able to infer \(x_{\textrm{HI}}\) at two redshifts: \(z\) \(\sim\) 6.7 and \(z\) \(\sim\) 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at \(z\) \(\sim\) 6.0 in order to constrain the intrinsic faint-end Ly\(\alpha\) EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyman-\(\alpha\) distribution from those of the IGM. We infer an upper limit of \(x_{\textrm{HI}}\) \(\leq\) 0.25 at \(z\) = 6.7 \(\pm\) 0.2 and a neutral fraction of \(x_{\textrm{HI}}\) = \(0.83^{+0.08}_{-0.11}\) at \(z\) = 7.6\(\pm\) 0.6, both within 1\(\sigma\) uncertainty, results which favor a moderately late and rapid reionization.
Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local universe, are usually traced by locating overdensities of galaxies. Large spectroscopic surveys of ...distant galaxies now exist, but their sensitivity depends mainly on a galaxy's star formation activity and dust content rather than its mass. Tracers of massive protoclusters that do not rely on their galaxy constituents are therefore needed. Here we report observations of Lyman-\(\alpha\) absorption in the spectra of a dense grid of background galaxies, which we use to locate a substantial number of candidate protoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that the structures producing the most absorption, most of which were previously unknown, contain surprisingly few galaxies compared to the dark matter content of their analogs in cosmological simulations. Nearly all are expected to be protoclusters, and we infer that half of their expected galaxy members are missing from our survey because they are unusually dim at rest-frame ultraviolet wavelengths. We attribute this to an unexpectedly strong and early influence of the protocluster environment on the evolution of these galaxies that reduced their star formation or increased their dust content.
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