Astrophysics and Astronomy Commons^™

A Bare Molecular Cloud At Z ~ 0.45*, Therese M. Jones, Toru Misawa, Jane C. Charlton, Andrew C. Mshar, Gary J. Ferland

Physics and Astronomy Faculty Publications

Several neutral species (Mg I, Si I, Ca I, Fe I) have been detected in a weak Mg II absorption line system (W_r (2796) ~ 0.15 Å) at z ~ 0.45 along the sightline toward HE0001-2340. These observations require extreme physical conditions, as noted in D'Odorico. We place further constraints on the properties of this system by running a wide grid of photoionization models, determining that the absorbing cloud that produces the neutral absorption is extremely dense (~100-1000 cm^-3), cold (< 100 K), and has significant molecular content (~72%-94%). Structures of this size and temperature have been detected in Milky Way CO surveys and have been predicted in hydrodynamic simulations of turbulent gas. In order to explain the observed line profiles in all neutral and singly ionized chemical transitions, the lines must suffer from unresolved saturation and/or the absorber must partially cover the broad emission line region of the background quasar. In addition to this highly unusual cloud, three other ordinary weak Mg II clouds (within densities of ~0.005 cm^-3 and temperatures of ~10, 000 K) lie within 500 km s^-1 along the …

Aztec Half Square Degree Survey Of The Shades Fields - I. Maps, Catalogues And Source Counts, J. E. Austermann, J. S. Dunlop, T. A. Perera, K. S. Scott, G. W. Wilson, I. Aretxaga, D. H. Hughes, O. Almaini, E. L. Chapin, S. C. Chapman, M. Cirasuolo, D. L. Clements, K. E.K. Coppin, L. Dunne, S. Dye, S. A. Eales, E. Egami, D. Farrah, D. Ferrusca, S. Flynn, D. Haig, M. Halpern, E. Ibar, R. J. Ivison, E. Van Kampen, Y. Kang, S. Kim, C. Lacey, James D. Lowenthal, P. D. Mauskopf, R. J. Mclure, A. M.J. Mortier

Astronomy: Faculty Publications

We present the first results from the largest deep extragalactic mm-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg , made at λ = 1.1 mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at λ = 850 μm with the Submillimetre Common-User Bolometer Array (SCUBA) in the SCUBA Half-Degree Extragalactic Survey (SHADES) project, namely the Lockman Hole East (mapped to a depth of 0.9-1.3 mJy rms) and the Subaru/XMM-Newton Deep Field (mapped to a depth of 1.0-1.7 mJy rms). …

Origins Of The Extragalactic Background At 1mm From A Combined Analysis Of The Aztec And Mambo Data In Goods-N, Kyle Penner, Alexandra Pope, Edward Chapin, Thomas Greve, Frank Bertoldi, Mark Brodwin, Ranga-Ram Chary, Christopher Conselice, Kristen Coppin, Mauro Giavalisco, David Hughes, Rob Ivison, Thushara Perera, Douglas Scott, Kimberly Scott, Grant Wilson

Scholarship

We present a study of the cosmic infrared background, which is a measure of the dust obscured activity in all galaxies in the Universe. We venture to isolate the galaxies responsible for the background at 1mm; with spectroscopic and photometric redshifts we constrain the redshift distribution of these galaxies. We create a deep 1.16mm map (sigma ~ 0.5mJy) by combining the AzTEC 1.1mm and MAMBO 1.2mm datasets in GOODS-N. This combined map contains 41 secure detections, 13 of which are new. By averaging the 1.16mm flux densities of individually undetected galaxies with 24um flux densities > 25uJy, we resolve 31--45 per …

Color-Magnitude Relation And Morphology Of Low-Redshift Ulirgs In Sloan Digital Sky Survey, Yuxi Chen, James D. Lowenthal, Min S. Yun

Astronomy: Faculty Publications

We present color-magnitude and morphological analysis of 54 low-redshift ultraluminous infrared galaxies (ULIRGs; 0.018 < z < 0.265 with z = 0.151), a subset of the Infrared Astronomical Satellite 1Jy sample, in the Sloan Digital Sky Survey (SDSS). The ULIRGs are both bright and blue: they are on average 1mag brighter in than the SDSS galaxies within the same redshift range, and 0.2mag bluer in g - r. They form a group in the color-magnitude diagram distinct from both the red sequence and the blue cloud formed by the SDSS galaxies: 24 out of the 52 unsaturated objects (46%) lie outside the 90% level number density contour of the SDSS galaxies. The majority (47, or 87%) have the colors typical of the blue cloud, and only four (7%) sources are located in the red sequence. While ULIRGs are popularly thought to be precursors to a QSO phase, we find few (three, or 6%) in the "green valley" where the majority of the X-ray- and IR-selected active galactic nuclei (AGNs) are found. Moreover, none of the AGN-host ULIRGs are found in the green valley. For the 14 previously spectroscopic identified AGNs (28%), we perform point-spread function subtractions and find that on average the central point sources contribute less than one-third to the total luminosity, and that their high optical luminosities and overall blue colors are apparently the result of star formation activity of the host galaxies. Visual inspection of the SDSS images reveals a wide range of morphologies including many close pairs, tidal tails, and otherwise disturbed profiles, in strong support of previous studies and the general view of ULIRGs as major mergers of gas-rich disk galaxies. A detailed morphology analysis using Gini and M coefficients shows that slightly less than one-half (42% in g band) of the ULIRGs are located in the merger region defined by morphology studies of local galaxies, while the remaining sources are located in the region of late-type and irregular galaxies. The heterogeneous distribution of ULIRGs in the G-M space is qualitatively consistent with the results found by numerical simulations of disk-disk mergers, and our study also shows that the measured morphological parameters are systematically affected by the signal-to-noise ratio and thus the merging galaxies can appear in various regions of the G-M parameter space. We briefly discuss the origins of the uncertainties and note that the morphology measurements should be implemented with caution for low physical resolution images. In general, our results reinforce the view that ULIRGs contain young stellar populations and are mergers in progress, but we do not observe the concentration of ULIRGs/AGN in the green valley as found by other studies. Our study provides a uniform comparison sample for studying dusty starbursts at higher redshifts such as Spitzer MIPS 24 μm-selected ULIRGs at z = 1-2 or submillimeter galaxies.

A Spectroscopically Confirmed Excess Of 24 Μm Sources In A Super Galaxy Group At Z=0.37: Enhanced Dusty Star Formation Relative To The Cluster And Field Environment, Kim-Vy H. Tran, Amelie Saintonge, John Moustakas, Lei Bai, Anthony H. Gonzalez, Bradford P. Holden, Dennis Zaritsky, Stefan Kautsch

Chemistry and Physics Faculty Articles

To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ~ 0.35. We draw on multi-wavelength observations that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ_1D = 303-580 km s^–1) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find …

Dynamics Of Lyman Break Galaxies And Their Host Halos, James D. Lowenthal, David C. Koo, Luc Simard, Eelco Van Kampen

Astronomy: Faculty Publications

We present deep two-dimensional spectra of 22 candidate and confirmed Lyman break galaxies (LBGs) at redshifts 2 < z < 4 in the Hubble Deep Field (HDF) obtained at the Keck II telescope. The targets were preferentially selected with spatial extent and/or multiple knot morphologies, and we used slitmasks and individual slits tilted to optimize measurement of any spatially resolved kinematics. Our sample is more than 1 mag fainter and is at higher redshift than the kinematic LBG targets previously studied by others. The median target magnitude was I814 = 25.3, and total exposure times ranged from 10 to 50 ks. We measure redshifts, some new, ranging from z = 0.2072 to z = 4.056, including two interlopers at z < 1, and resulting in a sample of 14 LBGs with a median redshift z = 2.424. The morphologies and kinematics of the close pairs and multiple knot sources in our sample are generally inconsistent with galaxy formation scenarios postulating that LBGs occur only at the bottom of the potential wells of massive host halos; rather, they support "collisional starburst" models with significant …

Chandra Observations Of Nuclear X-Ray Emission From Low Surface Brightness Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We present Chandra detections of X-ray emission from the active galactic nuclei (AGN) in two giant low surface brightness (LSB) galaxies, UGC 2936 and UGC 1455. Their X-ray luminosities are 1.8 × 1042 ergs s -1 and 1.1 × 1040 ergs s-1 respectively. Of the two galaxies, UGC 2936 is radio loud. Together with another LSB galaxy UGC 6614 (XMM-Newton archival data) both appear to lie above the X-ray-radio fundamental plane, and their AGN have black hole masses that are low compared to similar galaxies lying on the correlation. However, the bulges in these galaxies are well developed, and we …

Aztec Millimetre Survey Of The Cosmos Field - Ii. Source Count Overdensity And Correlations With Large-Scale Structure, J. E. Austermann, I. Aretxaga, D. H. Hughes, Y. Kang, S. Kim, James D. Lowenthal, T. A. Perera, D. B. Sanders, K. S. Scott, N. Scoville, G. W. Wilson, M. S. Yun

Astronomy: Faculty Publications

We report an overdensity of bright submillimetre galaxies (SMGs) in the 0.15 deg AzTEC/COSMOS survey and a spatial correlation between the SMGs and the optical-IR galaxy density at z ≲ 1.1. This portion of the COSMOS field shows a ∼3σ overdensity of robust SMG detections when compared to a background, or 'blank-field', population model that is consistent with SMG surveys of fields with no extragalactic bias. The SMG overdensity is most significant in the number of very bright detections (14 sources with measured fluxes S > 6 mJy), which is entirely incompatible with sample variance within our adopted blank-field number densities …

The Aztec/Sma Interferometric Imaging Survey Of Submillimeter-Selected High-Redshift Galaxies, Joshua D. Younger, Giovanni G. Fazio, Jia Sheng Huang, Min S. Yun, Grant W. Wilson, Matthew L.N. Ashby, Mark A. Gurwell, Alison B. Peck, Glen R. Petitpas, David J. Wilner, David H. Hughes, Itziar Aretxaga, Sungeun Kim, Kimberly S. Scott, Jason Austermann, Thushara Perera, James D. Lowenthal

Astronomy: Faculty Publications

We present results from a continuing interferometric survey of high-redshift submillimeter galaxies (SMGs) with the Submillimeter Array, including high-resolution (beam size ∼ 2 arcsec) imaging of eight additional AzTEC 1.1 mm selected sources in the COSMOS field, for which we obtain six reliable (peak signal-to-noise ratio (S/N) >5 or peak S/N >4 with multiwavelength counterparts within the beam) and two moderate significance (peak S/N >4) detections. When combined with previous detections, this yields an unbiased sample of millimeter-selected SMGs with complete interferometric follow up. With this sample in hand, we (1) empirically confirm the radio-submillimeter association, (2) examine the submillimeter …

Forming Early-Type Galaxies In Groups Prior To Cluster Assembly, Stefan Kautsch, Anthony H. Gonzalez, Christian A. Soto, Kim-Vy H. Tran, Dennis Zaritsky, John Moustakas

Chemistry and Physics Faculty Articles

We study a unique protocluster of galaxies, the supergroup SG1120–1202. We quantify the degree to which morphological transformation of cluster galaxies occurs prior to cluster assembly in order to explain the observed early-type fractions in galaxy clusters at z = 0. SG1120–1202 at z ~ 0.37 is composed of four gravitationally bound groups that are expected to coalesce into a single cluster by z = 0. Using HST ACS observations, we compare the morphological fractions of the supergroup galaxies to those found in a range of environments. We find that the morphological fractions of early-type galaxies (~60%) and the ratio …

Erasing Dark Matter Cusps In Cosmological Galactic Halos With Baryons, Emilio Romano-Diaz, Isaac Shlosman, Yehuda Hoffman, Clayton Heller

Physics & Astronomy: Faculty Publications

We study the central dark matter (DM) cusp evolution in cosmologically grown galactic halos. Numerical models with and without baryons (baryons+DM, hereafter BDM model, and pure DM, PDM model, respectively) are advanced from identical initial conditions, obtained using the Constrained Realization method. The DM cusp properties are contrasted by a direct comparison of pure DM and baryonic models. We find a divergent evolution between the PDM and BDM models within the inner few × 10 kpc region. The PDM model forms an R−1 cusp as expected, while the DM in the BDM model forms a larger isothermal cusp R …

SPitzer Irac Infrared Colours Of Submillimetre-Bright Galaxies, Min S. Yun, Itziar Aretxaga, Matthew L.N. Ashby, Jason Austermann, Giovanni G. Fazio, Mauro Giavalisco, Jia Sheng Huang, David H. Hughes, Sungeun Kim, James D. Lowenthal, Thushara Perera, Kim Scott, Grant Wilson, Joshua D. Younger

Astronomy: Faculty Publications

High-redshift submillimetre-bright galaxies identified by blank field surveys at millimetre and submillimetre wavelengths appear in the region of the Infra Red Array Camera (IRAC) colour-colour diagrams previously identified as the domain of luminous active galactic nuclei (AGNs). Our analysis using a set of empirical and theoretical dusty starburst spectral energy distribution (SED) models shows that power-law continuum sources associated with hot dust heated by young (≲100 Myr old), extreme starbursts at z > 2 also occupy the same general area as AGNs in the IRAC colour-colour plots. A detailed comparison of the IRAC colours and SEDs demonstrates that the two populations …

The Late Stellar Assembly Of Massive Cluster Galaxies Via Major Merging, Kim-Vy H. Tran, John Moustakas, Anthony H. Gonzalez, Lei Bai, Dennis Zaritsky, Stefan Kautsch

Chemistry and Physics Faculty Articles

We present multiwavelength observations of the brightest galaxies in four X-ray-luminous groups at z ~ 0.37 that will merge to form a cluster comparable in mass to Coma. Ordered by increasing stellar mass, the four brightest group galaxies (BGGs) present a time sequence where BGG-1, 2, and 3 are in merging systems and BGG-4 is a massive remnant (M_* = 6.7 × 10¹¹ M_☉). BGG-1 and 2 have bright, gravitationally bound companions and BGG-3 has two nuclei separated by only 2.5 kpc; thus, merging at z < 0.5 increases the BGG mass by ≳40% (t_MGR < 2 Gyr) and V-band luminosity by ~0.4 mag. The …

Evidence For A Population Of High-Redshift Submillimeter Galaxies From Interferometric Imaging, Joshua D. Younger, Giovanni G. Fazio, Jia Sheng Huang, Min S. Yun, Grant W. Wilson, Matthew L.N. Ashby, Mark A. Gurwell, Kamson Lai, Alison B. Peck, Glen R. Petitpas, David J. Wilner, Daisuke Iono, Kotaro Kohno, Ryohei Kawabe, David H. Hughes, Itziar Aretxaga, Tracy Webb, Alejo Martínez-Sansigre, Sungeun Kim, Kimberly S. Scott, Jason Austermann, Thushara Perera, James Lowenthal, Eva Schinnerer, Vernesa Smolčić

Astronomy: Faculty Publications

We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 μm with ∼2″ resolution. All of the sources - two radio-bright and five radio-dim - are detected as single point sources at high significance (>6 σ), with positions accurate to ∼0.2″ that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources …

Structure Formation Inside Triaxial Dark Matter Halos: Galactic Disks, Bulges, And Bars, Clayton Heller, Isaac Shlosman, Evangelie Athanassoula

Physics & Astronomy: Faculty Publications

We investigate formation and evolution of galactic disks immersed in assembling live DM halos. Models have been evolved from cosmological initial conditions and represent the collapse of an isolated density perturbation. The baryons include gas participating in star formation (SF) and stars with the energy feedback onto the ISM. We find that (1) the triaxial halo figure tumbling is insignificant and the angular momentum (J) is channeled into the internal circulation, while the baryonic collapse is stopped by the centrifugal barrier; (2) density response of the (disk) baryons is out of phase with DM, thus washing out the …

Spiral Disk Opacity From Occulting Galaxy Pairs In The Sloan Digital Sky Survey., Benne W. Holwerda, W. C. Keel, A. Bolton

Faculty and Staff Scholarship

A spiral galaxy partially overlapping a more distant elliptical offers a unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey (SDSS) DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z ¼ 0:0Y0:2 with the goal of determining the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk, and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will …

Stellar Populations Across The Ngc 4244 Truncated Galactic Disk., Roelof De Jong, A. C. Seth, D. Radburn-Smith, E. F. Bell, T. M. Brown, J. S. Bullock, S. Courteau, J. J. Dalcanton, H. C. Ferguson, P. Goudfrooij, S. Holfeltz, Benne W. Holwerda, C. Purcell, J. Sick, D. B. Zucker

Faculty and Staff Scholarship

We use the Hubble Space Telescope ACS to study the resolved stellar populations of the nearby, nearly edgeon galaxy NGC 4244 across its outer disk surface density break. The stellar photometry allows us to study the distribution of different stellar populations and reach very low equivalent surface brightnesses. We find that the break occurs at the same radius for young, intermediate-age, and old stars. The stellar density beyond the break drops sharply by a factor of at least 600 in 5 kpc. The break occurs at the same radius independent of height above the disk, but is sharpest in the …

Initial Mass Function Effects On The Colour Evolution Of Disk Galaxies, P. Westera, M. Samland, Stefan Kautsch, R. Buser, K. Ammon

Chemistry and Physics Faculty Articles

Aims. In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch.

Methods. We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours.

Results. We find that the effect of the IMF on the internal gas absorption is larger than its effect on …

The Metallicity Distribution Of Intracluster Stars In Virgo, Benjamin F. Willaims, Ted Von Hippel, Et Al.

Publications

We have used the Hubble Space Telescope's Advanced Camera for Surveys (ACS) to detect and measure ~5300 stars in a single intracluster field in the Virgo Cluster. By performing F606W and F814W photometry on these stars, we have determined their metallicity distribution function and constrained the types of stars present in this portion of Virgo's intracluster space. Based on the small number of stars detected that were brighter than the red giant branch (RGB) tip, we suggest that in this region, Virgo's intracluster stars are mostly old (10 Gyr). Through analysis of the RGB stars themselves, we determine that …

Virgo’S Intracluster Globular Clusters As Seen By The Advanced Camera For Surveys, Benjamin F. Williams, Robin Ciardullo, Ted Von Hippel, Et Al.

Publications

We report the discovery of four candidate intracluster globular clusters (IGCs) in a single deepHST ACS field of the Virgo Cluster. We show that each cluster is roughly spherical, has a magnitude near the peak of the Virgo globular cluster luminosity function, has a radial profile that is best fitted by a King model, and is surrounded by an excess of point sources that have the colors and magnitudes of cluster red giant stars. Despite the fact that two of our IGC candidates have integrated colors redder than the mean of the M87 globular cluster system, we propose that …

Evolution Of Stellar Bars In Live Axisymmetric Halos: Recurrent Buckling And Secular Growth, Inma Martinez-Valpuesta, Isaac Shlosman, Clayton Heller

Physics & Astronomy: Faculty Publications

Evolution of stellar bars in disk galaxies is accompanied by dynamical instabilities and secular changes. Following the vertical buckling instability, the bars are known to weaken dramatically and develop a pronounced boxy/ peanut shape when observed edge-on. Using high-resolution N-body simulations of stellar disks embedded in live axisymmetric dark matter halos, we have investigated the long-term changes in the bar morphology, specifically the evolution of the bar size, its vertical structure, and the exchange of angular momentum. We find that following the initial buckling, the bar resumes its growth from deep inside the corotation radius and follows the ultraharmonic resonance …

Measuring The Halo Mass Of Z ∼ 3 Damped Lyα Absorbers From The Absorber-Galaxy Cross-Correlation, Nicolas Bouché, Jeffrey P. Gardner, Neal Katz, David H. Weinberg, Romeel Davé, James D. Lowenthal

Astronomy: Faculty Publications

We test the reliability of a method to measure the mean halo mass of absorption-line systems such as damped Lyα absorbers (DLAs). The method is based on measuring the ratio of the cross-correlation between DLAs and galaxies to the autocorrelation of the galaxies themselves, which is (in linear theory) the ratio of their bias factor b. We show that the ratio of the projected cross- and autocorrelation functions [W (r )/w (r )] is also the ratio of their bias factor, irrespective of the galaxy distribution, provided that one uses the same galaxies for w (r ) and w (r …

The Star Formation Rate-Density Relationship At Redshift 3, Nicolas Bouché, James D. Lowenthal

Astronomy: Faculty Publications

We study the star formation rate (SFR) as a function of environment for UV-selected Lyman break galaxies (LBGs) at redshift 3. From deep [μ (sky) ≃ 27.6] UBVI MOSAIC images, covering a total of 0.90 deg , we select 334 LBGs in slices 100 h Mpc (comoving) deep spanning the redshift range 2.9 < z < 3.4 based on Bayesian photometric redshifts that include the I magnitude as a prior. The slice width (100 h Mpc) corresponds to the photometric redshift accuracy (Δ ∼ 0.15). We used mock catalogs from the GIF2 cosmological simulations to show that this redshift resolution is sufficient to statistically differentiate the high-density regions from the low-density regions using ∑ , the projected density to the fifth nearest neighbor. These mock catalogs have a redshift depth of 110 h Mpc, similar to our slice width. The large area of the MOSAIC images, ∼40 × 40 Mpc (comoving) per field, allows us to measure the SFR from the dust-corrected UV continuum as a function of ∑ . In contrast to low-redshift galaxies, we find that the SFR (or UV luminosity) of LBGs at z = 3 shows no detectable dependence on environment over 2 orders of magnitude in densities. To test the significance of our result, we use Monte Carlo simulations (from the mock catalogs) and the same projected density estimators that we applied to our data. We find that we can reject the steep z = 0 SFR-density relation at the 5 σ level. We conclude that the SFR-density relation at z = 3 must be at least 3.6 times flatter than it is locally; i.e., the SFR of LBGs is significantly less dependent on environment than the SFR of local star-forming galaxies. We find that the rest-frame UV colors are also independent of environment.

Galaxies At Z = 3 Around Damped Ly-Α Clouds, N. Bouché, James D. Lowenthal

Astronomy: Faculty Publications

We are exploring the connection between Damped Ly-α Absorption systems and Lyman Break Galaxies using deep m (5σ)=26 m - broad band imaging (UBVI) of four wide fields (0.25deg each) obtained at the Kitt Peak 4-m telescope with MOSAIC. Each field contains a DLA at z ∼ 3. We want to address the nature of DLA at high-redshifts: (1) Are the DLAs embedded in much larger systems of galaxies? (2) How does the spatial distribution of emitters in 3D (space and redshift) correlate with the absorber? Contrary to most previous DLA studies, we are not looking for the absorber, and …

Clustering Of Galaxies At Z ∼ 3 Around The Probable Damped Lyα Absorber Toward Qso Apm 08279+5255, Nicolas Bouché, James D. Lowenthal

Astronomy: Faculty Publications

We present results on the clustering of Lyman break galaxies (LBGs) around a probable damped Lyα absorption line cloud (DLA) at z = 2.974 from deep UBVI images of the field containing the quasar APM 08279+5255 (z = 3.91). The large area covered by our images, 0.31 deg or ∼40 × 40 Mpc comoving at redshift z = 3, and their depth, μ (sky) ≃ 27.6 mag arcsec , allow us to identify ∼450 LBG candidates brighter than I = 24.80 at 2. 75 < z < 3.25 both close (50 kpc) to the DLA line of sight and up to 20 Mpc (comoving) from the DLA, i.e., physically unrelated. LBG candidates were identified using photometric redshift techniques that include the I magnitude as a prior estimate in addition to the colors. The two are combined using Bayes's theorem. This helps to break the degeneracies that occur in a pure spectral template fitting scheme. The overall rms is σ ≃ 0.15 at z ∼ 3 based on our analysis of photometric redshifts in the HDF-N. From the redshift likelihood distributions, we selected LBG galaxies within a redshift slice of width W = 0.15(≃ σ ) centered on the redshift of the DLA z . Within that redshift slice, we find an enhancement of galaxies near the DLA using both the surface density (Σ/Σ ≃ 3) and an estimator of the three-dimensional spatial overdensity (n/n̄ ∼ 5 ± 3). The surface overdensity Σ/Σ is significant at the more than 95% significance level on scales 2.5 < r < 5 Mpc comoving. The overdensity cannot be related to the QSO environment since the QSO is at z = 3.91. These results imply that some DLA could reside in high-density regions. We search within 45″ from the line of sight for galaxies responsible for the DLA and find one candidate with Z = 3.03 that is 26″ (145 kpc physical) away. From its magnitude I = 24.65 ± 0.2, its luminosity is M = -21.35. Due to its large impact parameter, however, this galaxy is not a likely candidate for the absorber. abs em I,AB AB z z z abs g g g θ em phot I,AB 2 -2

Keck Spectroscopy And Imaging Of Faint Galaxies Identified As Microjansky Radio Sources, Nathan D. Roche, James D. Lowenthal, David C. Koo

Astronomy: Faculty Publications

We investigate the nature of the faintest radio sources detected in three Very Large Array surveys, to F(8.5 GHz) ∼ 8 μJy. Using the Keck low-resolution imaging spectrograph in BRI and the near-infrared camera in K′ (2.1 μm), we image 51 radio sources, and identify probable optical counterparts for 50. With low-resolution imaging spectroscopy, we successfully acquire new redshifts for 17 sources. Combining these with nine prior redshifts, we can then analyse a sample of 26 sources with spectroscopic redshifts. Based on this sample of 26, we find the largest contribution, about 60 per cent (15), to be from disc …

Gas Mass Fractions And The Evolution Of Low Surface Brightness Dwarf Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

The optical and H I properties are presented for a sample of low surface brightness (LSB) dwarf galaxies, cataloged from the Second Palomar Sky Survey. Gas mass fractions for LSB dwarfs reach the highest levels of any know galaxy type (fg = 95%), confirming that their low stellar densities are due to inefficient conversion of gas mass into stellar mass. Comparison with star formation models indicates that the blue optical colors of LSB dwarfs are not due to low metallicity or to recent star formation and can only be explained by a dominant stellar population less than 5 Gyr in …

Faint Radio Sources And Star Formation History, Deborah B. Haarsma, R. B. Partridge, R. A. Windhorst, E. A. Richards

University Faculty Publications and Creative Works

The centimeter-wave luminosity of local radio galaxies correlates well with their star formation rate. We extend this correlation to surveys of high-redshift radio sources to estimate the global star formation history. The star formation rate found from radio observations needs no correction for dust obscuration, unlike the values calculated from optical and ultraviolet data. Three deep radio surveys have provided catalogs of sources with nearly complete optical identifications and nearly 60% complete spectroscopic redshifts: the Hubble Deep Field and Flanking Fields at 12h + 62°, the SSA13 field at 13h + 42°, and the V15 field at 14h + 52°. …

Lyman-Α Imaging Of A Very Luminous Z = 2.3 Starburst Galaxy With Wfpc2, Nathan Roche, James D. Lowenthal, Bruce Woodgate

Astronomy: Faculty Publications

We investigate the Lyα and UV continuum morphology of one of the most luminous known Lymana emitting galaxies (the 'Coup Fourré Galaxy'), associated with a z = 2.3 damped Lyα absorption system in the spectrum of the QSO PHL 957. The galaxy is observed with the Hubble Space Telescope Wide-Field Planetary Camera 2 (HST WFPC2), through a narrow filter (F410M) corresponding to rest-frame Lyα for a total exposure time of 41.2 ks, plus shorter exposures in F555W and F814W. In all three passbands, the galaxy is resolved into a close (∼0.35 arcsec) pair of two components, CFgA and CFgB, both …

Star Formation And Tidal Encounters With The Low Surface Brightness Galaxy Ugc 12695 And Companions, Stacy S. Mcgaugh

Faculty Scholarship

We present VLA H I observations of the low surface brightness (LSB) galaxy UGC 12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy 2333 + 1234. UGC 12695 shows solid-body rotation but has a very lopsided morphology of the H I disk, with the majority of the H I lying in the southern arm of the galaxy. The H I column density distribution of this very blue LSB galaxy coincides in detail with its light distribution. Comparing the H I column density of UGC 12695 with the empirical (but not well-understood) value of Σc = 1021 …