Found 26 talks width keyword star forming galaxies
I will present the first Large Millimiter Telescope spectra of 4 nearby galaxies with known high star formation rates. The individual spectra were acquired with the Redshift Search Receiver, a 3 mm spectrograph that covers simultaneously the 3 mm band from 75 to 110 GHz. The spectra show rms temperatures of around 4 mK that allow us to detect not only common molecular species such as CO, HCN, HCO+, HCN, 13CO reported widely in the literature but also other more rare molecular transitions (HC3N, CN, CH3OH, CH3C2H) and even Hydrogen recombination lines (from H39alpha to H42alpha). We are making use of theoretical radiative transfer models to analize these spectra in order to understand the variations of the observed line ratios of different lines in galaxies classified as ultraluminous infrared galaxies where the star formation rate may be as high as 100 solar masses per year. These data will help to understand the physical conditions of the gas in regions that are forming stars very efficiently. The observed line ratios in star forming galaxies are also compared to those galaxies that is known to contain an AGN.
How does the group environment hamper star-formation in star-forming galaxies?
Abstract: We present the first results from the H-alpha Galaxy Groups Imaging Survey (HAGGIS), a narrow-band imaging survey of SDSS groups at z < 0.05 conducted using the Wide Field Imager (WFI) on the ESO/MPG 2.2 meter telescope and the Wide Field Camera (WFC) on the Issac Newton Telescope (INT). In total, we observed 100 galaxy groups with wide range of halo mass 10^12 - 10^14 M_sun in pairs of narrow-band filters selected to get continuum subtracted rest-frame H-alpha images for each galaxy in these groups. The excellent data allows us to detect H-alpha down to the 10^(-18) ergs/s/cm^2/arcsec^2 level. Here, we examine the role played by halo mass and galaxy stellar mass in deciding the overall star formation activity in star forming disks by comparing stacked H-alpha profiles of galaxies in different halo mass and stellar mass bins. With this preliminary study, we have found that the star-formation activity in star-forming galaxies decreases in larger halos compared to the field galaxies. Using median equivalent width profiles, we can infer how environmental processes affect star-forming galaxies differently at different radii.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is now performing scientific observations and the results of the second open observing cycle solicitation is about to be announced. With an available wavelength coverage from the visual to sub-mm wavelengths and a long life time - including planned instrument upgrades, SOFIA will provide critical resource for the astronomical community for the next decade and beyond. Current and expected SOFIA instruments provide heterodyne spectroscopy in the THz band, including the line of [O I], [C II] and [N II] as well as OH, HD and many other hydrides, at high spectral resolution. Echelle spectroscopy in the Mid-infrared (MIR) which will allow observations of e.g. fine-structure lines of and H2 pure rotational lines. These will help address questions of interstellar chemistry and physics in star forming regions, PDRs and galaxies. Mid-infrared (MIR) grism spectroscopy, of e.g. dust and ices, can be used to address questions of the freeze-out of molecules from the gas phase to better understand the formation, destruction and characteristics of interstellar ices. Imaging in the MIR and FIR and FIR polarimetry can provide a more complete picture of the temperature, density and magnetic field structure of e.g. star forming cores. I will highlight the current and expected capabilities of SOFIA and some of the early science results achieved.
In this talk we will show the evolution of high-redshift (z≥ 1.4) quiescent galaxies in the COSMOS field. We have studied an IRAC (mag 3.6 μm < 22.0) selected sample of ~ 18 000 galaxies at z≥ 1.4 in the COSMOS field with multiwavelength coverage extending from the U band to the Spitzer 24 μm one. We have derived accurate photometric redshifts and other important physical parameters [masses, ages and star formation rates (SFR)] through a SED-fitting procedure. Galaxies have been divided according to their star formation activity into actively star-forming, intermediate and quiescent galaxies depending on their specific star formation rate (sSFR = SFR/M). The evolution of the Galaxy Stellar Mass Funtion (GSMF) of the different populations, in particular of the quiescent galaxies, has been investigated in detail. There is a significant evolution of the quiescent stellar mass function from 2.5 < z < 3.0 to 1.4 < z < 1.6, increasing by ~1 dex in this redshift interval. We find that z ~1.5 is an epoch of transition of the GSMF: while the GSMF at z≳ 1.5 is dominated by the star-forming galaxies at all stellar masses, at z≲ 1.5 the contribution to the total GSMF of the quiescent galaxies is significant and becomes higher than that of the star-forming population for M≥ 1010.75 Msun. We derive the fraction of quiescent/star-forming galaxies with redshift, as well as the stellar mass density. We also compare our results with the predictions of theoretical models. Finally, I will introduce my current project: studying in deeper detail the IRAC drop-outs of the sample with new nIR (ULTRA-VISTA) and fIR (Herschel) data to elucidate between very dust-obscured objects or high-z star forming galaxies, which could help us to put some constrains to the high-mass end of the GSMF at high-z.
Morphologies of star-forming galaxies at z>1 are typically irregular containing a handful of dominant bright regions. Recent observational evidence suggest that many of these galaxies are governed by disc-like rotation. Using Halpha galaxy kinematics from OSIRIS+LGSAO we find that within z~1 turbulent discs star-forming regions have average sizes of 1.5 kpc and average Jeans masses of 4.2x10^9 \Msun, in total accounting for 20-30% of the stellar mass of the discs. These findings lend observational support to models that predict larger star-forming regions will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, high-z star-forming regions and HII regions are found to follow tight scaling relations over the range z=0-2 for Halpha size, velocity dispersion, luminosity and mass when comparing >2000 HII regions locally and 30 regions at z>1. While the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes likely govern their formation from high redshift to the current epoch. We are now able to test this conclusion with first results from a new sample of z=0.1-0.2 highly star-forming turbulent galaxies from the Sloan Digital Sky Survey.
Long Gamma-Ray Bursts are flashes of high-energy radiation and are linked to the death of massive stars. I will first summarize the main aspects of GRB astronomy, ranging from gamma to infrared frequencies, and secondly I will show how long GRBs pinpoint star-forming galaxies. Afterwards, I will present recent results which indicate as the GRB host population resembles all kind of star-forming galaxies, even the most dusty ones, almost invisible in optical-dedicated surveys.
Supermassive black holes are ubiquitous in galaxies and play a fundamental role in their life cycle. I will review observational progress in defining and refining the various empirical scaling relations between black hole masses and host galaxy properties. I will emphasize ways in which the intrinsic scatter of the scaling relations can be quantified, and present evidence that the scatter correlates with physical properties. I will describe how the scaling relations can be extended to active galaxies and summarize preliminary efforts to probe the evolution of these scaling relations with redshift. I will present new measurements of the cold ISM content in AGN host galaxies and constraints they place on currently popular models of AGN feedback. Lastly, I will discuss a new class of low-mass black holes in bulgeless and dwarf galaxies that serve as local analogs of seed supermassive black holes.
Luminous Infrared Galaxies (LIR=10^11-10^12Lsun) have star formation rates in the range of ~20-200Msun/yr. In the local Universe ~50% LIRGs show AGN or AGN/SB composite nuclear activity from optical spectroscopy. We decompose Spitzer/IRS 5-35micron spectra of a complete sample of 50 local (d<75Mpc) LIRGs using SB and AGN clumpy torus model templates. We derive a mid-IR AGN detection rate in our sample of local LIRGs of 50%. We also compare the continuum mid-IR AGN detection with other indicators in the mid-IR, optical and X-rays. We estimate for the first time the AGN bolometric contribution to the IR luminosity of the galaxies in local LIRGs. We find that one-third of local LIRGs have LAGN(bol)/LIR>0.05, with only ~10% having a significant contribution LAGN(bol)/LIR>0.25. This is in line with results of Nardini et al. (2010) that only at LIR>3x10^12Lsun the AGN starts dominating bolometrically the IR luminosity in the majority of the systems.
We present the detailed Star Formation History of the nearby Sculptor and Fornax dwarf spheroidal galaxies, from wide-field photometry of resolved stars, going down to the oldest Main Sequence Turn-Off. The accurately flux calibrated, wide-field Colour-Magnitude Diagrams are used directly in combination with spectroscopic metallicities of individual RGB stars to constrain the ages of different stellar populations, and derive the Star Formation History with particular accuracy.
The detailed Star Formation History shows the star formation at different ages and metallicities, at different positions in the galaxy, and shows that the known metallicity gradients are well matched to an age gradient. The obtained SFH is used to determine accurate age estimates for individual RGB stars, for which spectroscopic abundances (alpha-elements, r- and s-process elements) are known. In this way, we obtain the accurate age-metallicity relation of each galaxy, as well as the temporal evolution of alpha-element abundances.
This allows us to study, for the first time, the timescale of chemical evolution in these two dwarf galaxies, and determine an accurate age of the "knee" in the alpha-element distribution. Finally, we compare the timescale of chemical evolution in both dwarf galaxies, and determine whether the chemical abundance patterns seen in galaxies with recent episodes of star formation are a direct continuation of those with only old populations.
AbstractWhen we measure the electron density within an H II region using ratios of emission lines we find characteristic values in the range of 100-300 cm-3. But when we make these measurements using the total luminosity in Hα and the overall radial size of an H II region we find average values in the range 3-10. I will first explain how this discrepancy occurs, and then go on to show some measurements of electron densities in the H II regions of M51 (over 2500 regions) and the dwarf galaxy NGC 4449 (over 250 regions) using the second method, by Leonel Gutiérrez and myself. From these measurements we can infer how the electron density varies with the radial size of an individual region, and how it varies as we move from the center of the galaxy disc to the outside. Some interesting simple global relationships are found, which tell us about the interaction of star forming regions with their surroundings and how this interaction varies across the face of a galaxy.
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