Large Scale Structure in Dark Matter and Galaxies

Galaxy evolution and AGN growth in the early universe are believed to be strongly driven by merging (hierarchical growth) and galaxy dynamical interactions. Thus, a fall exploration of the environmental influences is absolutely essential to understanding this early evolution. The Cosmic Evolution Survey (COSMOS, [Scoville et al. 2007a]) is specifically designed to probe the correlated coevolution of galaxies, star formation, active galactic nuclei (AGN) and dark matter (DM) largescale structures (LSS) over the redshift range z > 0.5 to 6. The survey includes midti-wavelength imaging and spectroscopy from X-ray to radio wavelengths covering a 2 square degree equatorial field. Photometric redshifts are derived using 34 photometric UV-IR bands for 800,000 galaxies with accuracy reaching σ_z/(l +z) = 0.7 — 1.6% for bright galaxies (I_(AB) = 22 —24mag). Large scale structures have been traced in COSMOS from z = 0.2 to 2.5 in the baryons (from the galaxy density distribution) and in the dark matter to z = 1.1 (from weak tensing analysis of HST ACS images). These LSS extend over 20 Mpc with total mass up to ~10^(15)_ ⊙. The overall distribution of galaxy overdensities is similar with those predicted from the Millennium simulation. A trend for an increasing high overdensities at low z is clearly apparent in these data. At higher redshifts of z ~ 1, there appears to be a significant discrepancy between the observations and the simulations - with the simidations exhibiting earUer development of high density structores than is seen in the observed galaxy distributions. The observed galaxy spectral energy distributions (SEDs) and star formation rates (SFRs) clearly depend systematically on both redshift and environmental density - early SED types and lower SFRs in denser regions and at lower redshift. This evolution is probably driven by the exhaustion of the ISM and by galaxy interactions, the latter being strongly correlated with regions of highest dark matter density. Strong evolution is seen the frequency of close pairs of galaxies - particidarly for lower mass companions at projected separations 10 - 20 kpc

Evolution of ISM Contents of Massive Galaxies from z = 2 to 0.3

The mass of ISM in high redshift Galaxies is a major determinant of their morphology, star formation activity and how they will evolve to low redshift. Measurement of the CO lines at z > 0.5 are time consuming, even with the sensitivity of ALMA, and the derived ISM masses are subject to uncertainty in the CO-to-H_2 conversion factor. Here I describe a much faster technique— measuring the long wavelength Rayleigh-Jeans dust emission using the spectacular continuum sensitivity of ALMA. Using a metallicity-dependent gas-to-dust abundance ratio derived from studies of low-z galaxies, one then obtains the ISM mass. Initial results from our ALMA Cycle-0 observations are presented for a small sample of stellar-mass selected galaxies in COSMOS. This technique will enable measurement of 100's of galaxies at high-z with observations of typically ∼10 min per galaxy

ALMA: HI and He^+ Lines and Dust in Starbursts, AGN and High-z Galaxies

We describe preliminary results for two ALMA projects – 1) imaging the HCN(4-3) line and H26α lines in Arp 220 and 2) measurements of the dust continuum in a sample of 107 high redshift galaxies to probe the evolution of the ISM masses. The HCN observations in Arp 220 at 1/2″ resolution provide the first high resolution imaging of the dense star forming gas in this prototypical ULIRG. The HCN is seen in two clearly delineated, counter-rotating disks. The H26α line is a definitive probe of the star formation rate in Arp 220, avoiding obscuration by dust and contamination by AGN luminosity contributions. In the second project, the remarkable continuum sensitivity of ALMA in Band 7 is used to measure the long wavelength Rayleigh-Jeans tail of the dust emission from a sample of 120 galaxies in COSMOS at z = 0.3 to 2.2, providing estimates for the dust masses and hence their ISM masses. This technique will enable measurements for hundreds of galaxies at high-z with observations of typically ~10 min per galaxy. This is in contrast to CO line imaging which typically requires a few hours per galaxy even with the sensitivity of ALMA. The dust-based mass estimates also avoid the uncertainties associated with the CO-to-H2 conversion factor

The Redshift Evolution of Bulges and Disks of Spiral Galaxies in COSMOS

We present a preliminary analysis of the bulge and disk properties for a sample of over 4000 L* spiral galaxies at z < 0.84 from the COSMOS 2 square degree survey. We find that for early Hubble type spiral galaxies (Sa–Sb), the bulge-to-disk ratio is roughly constant over the last 7 Gyr of lookback time. This suggests that bulges of early type spirals were in place early on, consistent with other downsizing signatures. There is a monotonic increase in the bulge-to-disk ratios of late type spirals but that likely reflects the well-known decline in the star formation rate from z ~ 1 to the present. For this sample of L* spirals, we also find that the median exponential scale length of disks remains unchanged at 3.1 kpc from z = 0.0 to z = 0.84

IRAC Deep Survey of COSMOS

Over the last four years, we have developed the COSMOS survey field with complete multi-wavelength coverage from radio to X-ray, including a total of 600 hours of Spitzer Legacy time (166 hours IRAC, 460 hours MIPS). Here we propose to deepen the IRAC 3.6 µm and 4.5 µm coverage with 3000 hours over 2.3 deg^2 area included in deep Subaru imaging. This extended mission deep survey will increase the sensitivity by a factor of 3–5. The most important impact will be that the COSMOS survey will then provide extremely sensitive photometric redshifts and stellar mass estimates for approximately a million galaxies out to z~6. We expect these data to detect approximately 1000 objects at z = 6 to 10. The data will also provide excellent temporal coverage for variability studies on timescales from days to the length of the extended mission

OH-IR stars. I. Physical properties of circumstellar envelopes

A theoretical model of the circumstellar envelope which surrounds a OH-IR star is developed. The circumstellar gas is ejected by radiation pressure which acts on dust grains that condense in the atmosphere of the central star. The dust grains transfer momentum to the gas by collisions with the gas molecules. These collisions are the dominant source of heat input to the circumstellar gas. The major sources of cooling are the emission of radiation by H_2O molecules and adiabatic expansion. The gas temperature decreases from T ≈ 2 x 10^3 K near the stellar surface at r ≈ 6 x 10^(13) cm, to T ≈ 8 x 10^2 K at r = 10^(15) cm and to T ≈ 10^2 K at r = 10^(16) cm. The OH molecule abundance in the circumstellar envelope is controlled by chemical exchange reactions and by the dissociation of H^2O molecules. The reaction OH + H_2 ↔ H_2O + H + 0.69 eV, which has an activation energy of 0.3 eV, rapidly converts OH molecules into H_2O molecules in the warm (T ≳ 5 x 10^2 K) inner (r ≾ 2 x 10^(15) cm) region of the circumstellar envelope. Beyond r ≈ 2 x 10^(15) cm, T is so low that the exchange reaction is very slow and the mean lifetime of an OH molecule is greater than the expansion time scale for the circumstellar envelope. In the outer region of the circumstellar envelope, OH molecules are produced from the photodissociation of H_2O molecules by the interstellar ultraviolet radiation and from the dissociation of H_2O molecules by collisions with dust grains. These processes are capable of producing OH number densities greater than 1 cm^(-3) at r ≈ 10^(16) cm. The predicted values of the gas temperature, T, and the OH abundance, n_(OH), depend upon the rate of mass loss from the central star, Ф. The results quoted above are based on a calculation with Ф = 3 x 10^(-5) M_☉ yr^(-1). In general, T varies inversely and n_(OH) varies directly with Ф

What Lurks in ULIRGs?—Probing the Chemistry and Excitation of Molecular Gas in the Nuclei of Arp 220 and NGC 6240

We have imaged the dense star-forming regions of Arp 220 and NGC 6240 in the 3 mm band transitions of CO, HCN, HCO^+, HNC, and CS at 0farcs5–0farcs8 resolution using CARMA. Our data set images all these lines at similar resolutions and high sensitivity, and can be used to derive line ratios of faint high excitation lines. In both the nuclei of Arp 220, the HCN/HNC ratios suggest chemistry of X-ray Dominated Regions (XDRs)—a likely signature of an active galactic nucleus. In NGC 6240, there is no evidence of XDR type chemistry, but there the bulk of the molecular gas is concentrated between the nuclei rather than on them. We calculated molecular H_2 densities from excitation analysis of each of the molecular species. It appears that the abundances of HNC and HCO^+ in Ultra Luminous Infrared Galaxies may be significantly different from those in galactic molecular clouds. The derived H_2 volume densities are ~5 × 10^4 cm^(−3) in the Arp 220 nuclei and ~10^4 cm^(−3) in NGC 6240

Highest Redshift Image of Neutral Hydrogen in Emission: A CHILES Detection of a Starbursting Galaxy at z = 0.376

Our current understanding of galaxy evolution still has many uncertainties associated with the details of the accretion, processing, and removal of gas across cosmic time. The next generation of radio telescopes will image the neutral hydrogen (H i) in galaxies over large volumes at high redshifts, which will provide key insights into these processes. We are conducting the COSMOS H i Large Extragalactic Survey (CHILES) with the Karl G. Jansky Very Large Array, which is the first survey to simultaneously observe H i from z = 0 to z ~ 0.5. Here, we report the highest redshift H i 21 cm detection in emission to date of the luminous infrared galaxy COSMOS J100054.83+023126.2 at z = 0.376 with the first 178 hr of CHILES data. The total H i mass is (2.9 ± 1.0) × 10^(10) M_⊙ and the spatial distribution is asymmetric and extends beyond the galaxy. While optically the galaxy looks undisturbed, the H i distribution suggests an interaction with a candidate companion. In addition, we present follow-up Large Millimeter Telescope CO observations that show it is rich in molecular hydrogen, with a range of possible masses of (1.8–9.9) × 10^(10) M_⊙. This is the first study of the H i and CO in emission for a single galaxy beyond z ~ 0.2

Radiative Trapping and Hyperfine Structure: HCN

The anomalous weakness of the F = 1 → 1 hyperfine component in the J = 1 → 0 emission of interstellar HCN can be caused by radiative trapping in the J = 2 → 1 lines. The anomaly is readily produced if the J = 1 levels are populated largely by collisional excitation from J = 0 to J = 2 followed by radiative decay to J = 1 with the J = 2 → 1 lines optically thick. Regions where the anomaly is found probably have H_2 densities less than 10s^5 cm^(-3) and optical depths in the J =1 → 0 lines greater than 50

On the Origin of the 10 Micron Depressions in the Spectra of Compact Infrared Sources

The 10 µ depression observed in the spectrum of a compact infrared object is usually ascribed to absorption by intervening cold silicate grains, and the underlying source spectrum is taken to be either a blackbody or a blackbody with superposed excess 10 µ emission. We question this assumption of the underlying source spectrum for optically thick compact sources. We find, upon modeling both the objects BN and W3 IRS5, that the source actually emits less at the 10 µ resonance than outside the resonance, so that a depression at 10 µ already exists in the source spectrum. This difference in emission arises because, due to the higher opacity in the resonance, the observed 10 µ radiation is produced further out in the source than is the radiation just outside the resonance. And the lower dust temperature further out gives rise to a weaker emission at 10 µ than in the continuum. An observed 10 µ depression can be largely due to this effect, and little or no intervening extinction is required. This explanation of the 10 µ depression leads to a correlation such that the magnitude of depression will increase with decreasing color temperature of the source. It also predicts no depression at 20 µ for sources with color temperatures greater than 200 K. Observations at 20 µ would then be able to decide on the validity of this explanation