We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large program that is gathering high quality HI-line spectra using the Arecibo radio telescope for an unbiased sample of ~1000 galaxies with stellar masses greater than 10^10 Msun and redshifts 0.025
We present integral field spectroscopy observations of two star-forming dwarf galaxies in the Virgo cluster (VCC135 and VCC324) obtained with PMAS/PPak at the Calar Alto 3.5 meter telescope. We derive metallicity maps using the N2 empirical calibrator. The galaxies show positive gas metallicity gradients, contrarily to what is usually found in other dwarfs or in spiral galaxies. We measure gradient slopes of 0.20 $\pm$ 0.06 and 0.15 $\pm$ 0.03 dex/$R_e$ for VCC135 and VCC324, respectively. Such a trend has been only observed in few, very isolated galaxies, or at higher redshifts ($z >$ 1). It is thought to be associated with accretion of metal-poor gas from the intergalactic medium, a mechanism that would be less likely to occur in a high-density environment like Virgo. We combine emission line observations with deep optical images to investigate the origin of the peculiar metallicity gradient. The presence of weak underlying substructures in both galaxies and the analysis of morphological diagnostics and of ionised gas kinematics suggest that the inflow of metal-poor gas to the central regions of the dwarfs may be related to a recent merging event with a gas-rich companion.
Abstract I will present the result of two observational projects using ALMA to investigate the properties of the molecular gas in low-redshift ( z ∼ 0.2) ultraviolet-luminous galaxies. These objects are extremely dense, highly star-forming and very metal-poor compared to other galaxies of similar stellar mass at the same redshifts, justifying their use as analogues to distant main-sequence galaxies in an attempt to understand the interplay between gas and star formation under similar conditions in the early universe. Firstly, we have observed the most metal-poor objects in our sample, in order to determine whether metallicity plays a role in CO emissivity of the molecular regions in these galaxies. Our four non-detections, with stringent upper limits, shows that CO is severely depleted, even under turbulent conditions. We have also observed one object with high spatial resolution, comparing data from CO emission and hydrogen recombination lines down to a resolution of ∼ 400 pc, allowing for a detailed analysis of the conversion of gas into new stars. We are able to compare star formation laws in individual clumps and the surrounding ISM, highlighting the difference between star formation efficiencies in each environment within the galaxy. Finally, the high-resolution data offers interesting insights on the growth of supermassive black holes in these galaxies: our combined multiwavelength data shows that there must be a low-mass (105 M ȯ ) black hole in the center of the galaxy, while bolometric luminosity in the central region is dominated by star formation activity.
We present data from Integral Field Spectroscopy for three supercompact UV-Luminous Galaxies (ScUVLGs). As nearby (z ∼ 0.2) compact (R50 ∼ 1–2 kpc) bright Paschen-α sources, with unusually high star formation rates (SFR = 3–100 M☉ yr−1), ScUVLGs are an ideal population for studying detailed kinematics and dynamics in actively star-forming galaxies. In addition, ScUVLGs appear to be excellent analogs to high-redshift Lyman Break Galaxies (LBGs), and our results may offer additional insight into the dynamics of LBGs. Previous work by our team has shown that the morphologies of these galaxies exhibit tidal features and companions, and in this study we find that the dynamics of ScUVLGs are dominated by disturbed kinematics of the emission line gas—suggesting that these galaxies have undergone recent feedback, interactions, or mergers. While two of the three galaxies do display rotation, v/σ<1—suggesting dispersion-dominated kinematics rather than smooth rotation. We also simulate how these observations would appear at z ∼ 2. Lower resolution and loss of low surface brightness features cause some apparent discrepancies between the low-z (observed) and high-z (simulated) interpretations and quantitatively gives different values for v/σ, yet simulations of these low-z analogs manage to detect the brightest regions well and resemble actual high-z observations of LBGs.
Abstract How is gas converted into stars across cosmic time? Observations of star-forming galaxies at high redshift indicate that the conditions of the interstellar medium (ISM) were remarkably distinct from typical spirals in the local universe. Nevertheless, these observations are biased towards objects brighter than L*, due to the large luminosity distances involved. Here I present a survey targeting the molecular gas in galaxies at low redshift ( z ~ 0.2) with ISM conditions remarkably similar to those observed at earlier epochs, including high star formation rates and lower metallicities. CO observations performed with CARMA indicate that these galaxies follow the same star-formation law as local spirals and other galaxies at the same redshift, albeit at much higher densities. We also present recent results from our ALMA program studying galaxies down to 12 + log(O/H) ~ 8, and discuss the implications of these data to our understanding of the molecular gas reservoir and the conversion factor between CO luminosity and gas mass in environments that are simultaneously low in metal content and extremely dense.
Abstract The bimodality in galaxy properties has been observed at low and high redshift, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this work, we present a study of over 100 transiting galaxies in the so-called “green valley” at intermediate redshifts ( z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope, we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the Universe was half its current age. Our results indicate that the process happened more rapidly, affecting more massive galaxies in the past, suggesting a top-down scenario whereby the massive end of the red sequence assembles first. This represents another aspect of downsizing, with the mass flux density moving towards smaller galaxies in recent times.
We present the first integral-field spectroscopic observations of high-redshift submillimeter-selected galaxies (SMGs) using Laser Guide Star Adaptive Optics (LGS-AO). We target H-alpha emission of three SMGs at redshifts z~1.4-2.4 with the OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) on Keck. The spatially-resolved spectroscopy of these galaxies reveals unresolved broad H-alpha line regions (FWHM>1000 km/s) likely associated with an AGN and regions of diffuse star formation traced by narrow-line H-alpha emission (FWHM<500 km/s) dominated by multiple Halpha-bright stellar clumps, each contributing 1-30% of the total clump-integrated H-alpha emission. We find that these SMGs host high star-formation rate surface densities, similar to local extreme sources, such as circumnuclear starbursts and luminous infrared galaxies. However, in contrast to these local environments, SMGs appear to be undergoing such intense activity on significantly larger spatial scales as revealed by extended H-alpha emission over 4-16 kpc. H-alpha kinematics show no evidence of ordered global motion as would be found in a disk, but rather large velocity offsets (~few x 100 km/s) between the distinct stellar clumps. Together with the asymmetric distribution of the stellar clumps around the AGN in these objects, it is unlikely that we are unveiling a clumpy disk structure as has been suggested in other high-redshift populations of star-forming galaxies. The SMG clumps in this sample may correspond to remnants of originally independent gas-rich systems that are in the process of merging, hence triggering the ultraluminous SMG phase.
Disk galaxies viewed as thin planar structures resulting from the conservation of angular momentum of an initially rotating pre-galactic cloud allow merely a first-order model of galaxy formation. Still, the presence of vertically extended structures has allowed us to gather a deeper understanding of the richness in astrophysical processes (e.g., minor mergers, secular evolution) that ultimately result in the observed diversity in disk galaxies and their vertical extensions. We measure the stellar disk scale height of 46 edge-on spiral galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) project. This paper aims to investigate the radial variation of the stellar disk vertical scale height and the existence of the so-called thick disk component in our sample. The measurements were done using one-, two-, and three-dimensional profile fitting techniques using simple models. We found that two-thirds of our sample shows the presence of a thick disk, suggesting that these galaxies have been accreting gaseous material from their surroundings. We found an average thick-to-thin disk scale height ratio of 2.65, which agrees with previous studies. Our findings also support the disk flaring model, which suggests that the vertical scale height increases with radius. We further found good correlations: between the scale height $h_{z}$ and the scale length and between $h_z$ and the optical de Vaucouleurs radius $R_{25}$.
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