AEGIS: Extinction and Star Formation Tracers from Line Emission

Strong nebular emission lines are a sensitive probe of star formation and extinction in galaxies, and the [O II] line detects star forming populations out to z>1. However, star formation rates from emission lines depend on calibration of extinction and the [O II]/H-alpha line ratio, and separating star formation from AGN emission. We use calibrated line luminosities from the DEEP2 survey and Palomar K magnitudes to show that the behavior of emission line ratios depends on galaxy magnitude and color. For galaxies on the blue side of the color bimodality, the vast majority show emission signatures of star formation, and there are strong correlations of extinction and [O II]/H-alpha with restframe H magnitude. The conversion of [O II] to extinction-corrected H-alpha and thus to star formation rate has a significant slope with M_H, 0.23 dex/mag. Red galaxies with emission lines have a much higher scatter in their line ratios, and more than half show AGN signatures. We use 24 micron fluxes from Spitzer/MIPS to demonstrate the differing populations probed by nebular emission and by mid-IR luminosity. Although extinction is correlated with luminosity, 98% of IR-luminous galaxies at z~1 are still detected in the [O II] line. Mid-IR detected galaxies are mostly bright and intermediate color, while fainter, bluer galaxies with high [O II] luminosity are rarely detected at 24 microns.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letters AEGIS special editio

Pulmonary tuberculosis in the central prison of Douala, Cameroon

Objective: To determine the prevalence of and factors associated with pulmonary tuberculosis (PTB) in an urban prison in sub-Saharan Africa.Design: A cross-sectional survey. Setting: The Central Prison of Douala, Cameroon. Results: Two thousand four hundred and seventy four (87.4%) out of 2830 inmates underwent screening. Twenty seven (1.1%) of the inmates were under treatment for smear-positive PTB on commencement of the survey while 60 (2.4%) were diagnosed with smear and/or culture-positive PTB during the active case finding, resulting in a point prevalence of PTB of 3.5%. HIV seroprevalence in inmates without clinical signs of PTB was 111/1067 (10.4%) while it amounted to 6/24 (25%) in PTB patients. In multiple stepwise regression analysis, a low BMl, a prison stay of ≤12 months, and a history of previous incarceration were positively associated with PTB. Conclusion: The study results confirm the high prevalence rates of PTB in prison populations and underscore the need for urgent preventive measures. East African Medical Journal Vol. 83(1) 2006: 25-3

The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit

The structural properties of the low surface brightness stellar host in blue compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer regions of their radial profiles. The limitations imposed by the presence of a large starburst emission overlapping the underlying component makes this kind of analysis a difficult task. We propose a two-dimensional fitting methodology in order to improve the extraction of the structural parameters of the LSB host. We discuss its advantages and weaknesses by using a set of simulated galaxies and compare the results for a sample of eight objects with those already obtained using a one-dimensional technique. We fit a PSF convolved Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R filters. We restrict the fit to the stellar host by masking out the starburst region and take special care to minimize the sky-subtraction uncertainties. In order to test the robustness and flexibility of the method, we carry out a set of fits with synthetic galaxies. Furthermore consistency checks are performed to assess the reliability and accuracy of the derived structural parameters. The more accurate isolation of the starburst emission is the most important advantage and strength of the method. Thus, we fit the host galaxy in a range of surface brightness and in a portion of area larger than in previous published 1D fits with the same dataset. We obtain robust fits for all the sample galaxies, all of which, except one, show Sersic indices n very close to 1, with good agreement in the three bands. These findings suggest that the stellar hosts in BCDs have near-exponential profiles, a result that will help us to understand the mechanisms that form and shape BCD galaxies, and how they relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in A&A. A higher resolution version of the figures can be provided upon reques

Star Formation in AEGIS Field Galaxies since z=1.1 : The Dominance of Gradually Declining Star Formation, and the Main Sequence of Star-Forming Galaxies

We analyze star formation (SF) as a function of stellar mass (M*) and redshift z in the All Wavelength Extended Groth Strip International Survey (AEGIS). For 2905 field galaxies, complete to 10^10(10^10.8) Msun at z<0.7(1), with Keck spectroscopic redshifts out to z=1.1, we compile SF rates (SFR) from emission lines, GALEX, and Spitzer MIPS 24 micron photometry, optical-NIR M* measurements, and HST morphologies. Galaxies with reliable signs of SF form a distinct "main sequence (MS)", with a limited range of SFR at a given M* and z (1 sigma < +-0.3 dex), and log(SFR) approximately proportional to log(M*). The range of log(SFR) remains constant to z>1, while the MS as a whole moves to higher SFR as z increases. The range of SFR along the MS constrains the amplitude of episodic variations of SF, and the effect of mergers on SFR. Typical galaxies spend ~67(95)% of their lifetime since z=1 within a factor of <~ 2(4) of their average SFR at a given M* and z. The dominant mode of the evolution of SF since z~1 is apparently a gradual decline of the average SFR in most individual galaxies, not a decreasing frequency of starburst episodes, or a decreasing factor by which SFR are enhanced in starbursts. LIRGs at z~1 seem to mostly reflect the high SFR typical for massive galaxies at that epoch. The smooth MS may reflect that the same set of few physical processes governs star formation prior to additional quenching processes. A gradual process like gas exhaustion may play a dominant role.Comment: 5 pages, 1 figure, emulateapj; ApJ Letters, accepted; AEGIS special issue; proof-level corrections added; title change

The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip

We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.Comment: 24 pages, including 3 tables and 18 color figures; accepted to the Astrophysical Journal; high resolution version available at http://www.noao.edu/noao/staff/lotz/lotz_mergers.pd

Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications for Red Galaxy Formation

The DEEP2 and COMBO-17 surveys are used to study the evolution of the luminosity function of red and blue galaxies to $z \sim 1$. Schechter function fits show that, since $z = 1$, $M^*_B$ dims by $\sim$ 1.3 mag per unit redshift for both color classes, $\phi^*$ of blue galaxies shows little change, while $\phi^*$ for red galaxies has formally nearly quadrupled. At face value, the number density of blue galaxies has remained roughly constant since $z = 1$, whereas that of red galaxies has been rising. Luminosity densities support both conclusions, but we note that most red-galaxy evolution occurs between our data and local surveys and in our highest redshift bin, where the data are weakest. We discuss the implications of having most red galaxies emerge after $z = 1$ from precursors among the blue population, taking into account the properties of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue galaxies have their star-formation quenched in gas-rich mergers, migrate to the red sequence with a variety of masses, and merge further on the red sequence in one or more purely stellar mergers. E/S0s of a given mass today will have formed via different routes, in a manner that may help to explain the fundamental plane and other local scaling laws.Comment: Submitted to ApJ. 73 pages, 12 figures. Part II of a two-paper series. The entire paper is available as a single postscript file at: http://www.ucolick.org/~cnaw/paper2_submitted.ps.g

Star formation in AEGIS field galaxies since z=1.1 . Staged galaxy formation, and a model of mass-dependent gas exhaustion

We analyze star formation (SF) as a function of stellar mass (M_*) and redshift z in the All Wavelength Extended Groth Strip International Survey (AEGIS), for star-forming field galaxies with M_* >~ 10^10 M_sun out to z=1.1. The data indicate that the high specific SF rates (SFR) of many less massive galaxies do not represent late, irregular or recurrent, starbursts in evolved galaxies. They rather seem to reflect the onset (initial burst) of the dominant SF episode of galaxies, after which SF gradually declines on Gyr timescales to z=0 and forms the bulk of a galaxy's M_*. With decreasing mass, this onset of major SF shifts to decreasing z for an increasing fraction of galaxies (staged galaxy formation). This process may be an important component of the ``downsizing'' phenomenon. We find that the predominantly gradual decline of SFR (Noeske et al. 2007, this volume) can be reproduced by exponential SF histories (tau models), if less massive galaxies have systematically longer e-folding times tau, and a later onset of SF (z_f). Our model can provide a first parametrization of SFR as a function of M_* and z, and quantify mass-dependences of tau and z_f, from direct observations of M_* and SFR up to z>1. The observed evolution of SF in galaxies can plausibly reflect the dominance of gradual gas exhaustion. The data are also consistent with the history of cosmological accretion onto Dark Matter halos.Comment: 5 pages, 2 figures, emulateapj; ApJ Letters, accepted; AEGIS special issue; proof-level corrections added; removed former footnote 10 (erroneous

Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3

Although giant clumps of stars are crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we study the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the HII regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of SFGs that contain at least one off-center clump (Fclumpy) and the contributions of clumps to the rest-frame UV light and star formation rate of SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass (log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from 55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the Fclumpy trend of massive galaxies; (2) minor mergers are a viable explanation of the Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at all redshifts, possibly linked to the molecular gas fraction of the galaxies. (Abridged)Comment: 22 pages, 15 figures. Appeared in ApJ (2015, 800, 39). A few typos correcte

3D Spectroscopy of Local Luminous Compact Blue Galaxies: Kinematics of NGC 7673

The kinematic properties of the ionized gas of local Luminous Compact Blue Galaxy (LCBG) NGC 7673 are presented using three dimensional data taken with the PPAK integral field unit at the 3.5-m telescope in the Centro Astron\'omico Hispano Alem\'an. Our data reveal an asymmetric rotating velocity field with a peak to peak difference of 60 km s$^{-1}$. The kinematic centre is found to be at the position of a central velocity width maximum ($\sigma=54\pm1$ km s$^{-1}$), which is consistent with the position of the luminosity-weighted centroid of the entire galaxy. The position angle of the minor rotation axis is 168$^{\circ}$ as measured from the orientation of the velocity field contours. At least two decoupled kinematic components are found. The first one is compact and coincides with the position of the second most active star formation region (clump B). The second one is extended and does not have a clear optical counterpart. No evidence of active galactic nuclei activity or supernovae galactic winds powering any of these two components has been found. Our data, however, show evidence in support of a previously proposed minor merger scenario in which a dwarf galaxy, tentatively identified with clump B, is falling into NGC 7673. and triggers the starburst. Finally, it is shown that the dynamical mass of this galaxy may be severely underestimated when using the derived rotation curve or the integrated velocity width, under the assumption of virialization.Comment: Accepted for publication by MNRAS. The paper contains 10 figures and 2 table

POX 186: A Dwarf Galaxy in the Process of Formation?

We present deep U, V and I band images of the "ultracompact" blue dwarf galaxy POX 186 obtained with the Planetary Camera 2 of the Hubble Space Telescope. We have also obtained a near-ultraviolet spectrum of the object with the Space Telescope Imaging Spectrograph, and combine this with a new ground-based optical spectrum. The images confirm the galaxy to be extremely small, with a maximum extent of only 300 pc, a luminosity ~ 10^-4 L*, and an estimated mass ~ 10^7 M(sun). Its morphology is highly asymmetric, with a tail of material on its western side that may be tidal in origin. The U-band image shows this tail to be part of a stream of material in which stars have recently formed. Most of the star formation in the galaxy is however concentrated in a central, compact (d ~ 10 - 15 pc) star cluster. The outer regions of the galaxy are significantly redder than the cluster, with V - I colors consistent with a population dominated by K and M stars. While these results rule out earlier speculation that POX 186 is a protogalaxy, its morphology, mass and active star formation suggest that it represents a recent (within ~ 10^8 yr) collision between two clumps of stars of sub-galactic size (~ 100 pc). POX 186 may thus be a very small dwarf galaxy that, dynamically speaking, is still in the process of formation. This interpretation is supported by the fact that it resides in a void, so its morphology cannot be explained as the result of an encounter with a more massive galaxy. Clumps of stars this small may represent the building blocks required by hierarchical models of galaxy formation, and these results also support the recent "downsizing" picture of galaxy formation in which the least massive objects are the last to form.Comment: accepted for publication in ApJ; 23 pages, 5 figure