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Sarzi, Marc,Shields, Joseph C.,Schawinski, Kevin,Jeong, Hyunjin,Shapiro, Kristen,Bacon, Roland,Bureau, Martin,Cappellari, Michele,Davies, Roger L.,Tim de Zeeuw, P.,Emsellem, Eric,Falcó,n-Barroso Blackwell Publishing Ltd 2010 Monthly notices of the Royal Astronomical Society Vol.402 No.4
<P>ABSTRACT</P><P>Following our study on the incidence, morphology and kinematics of the ionized gas in early-type galaxies, we now address the question of what is powering the observed nebular emission. To constrain the likely sources of gas excitation, we resort to a variety of ancillary data we draw from complementary information on the gas kinematics, stellar populations and galactic potential from the <SMALL>SAURON</SMALL> data, and use the <SMALL>SAURON</SMALL>-specific diagnostic diagram juxtaposing the [O <SMALL>III</SMALL>]λ5007/Hβ and [N <SMALL>I</SMALL>]λλ5197, 5200/Hβ line ratios. We find a tight correlation between the stellar surface brightness and the flux of the Hβ recombination line across our sample, which points to a diffuse and old stellar source as the main contributor of ionizing photons in early-type galaxies, with post-asymptotic giant branch (pAGB) stars being still the best candidate based on ionizing balance arguments. The role of AGN photoionization is confined to the central 2–3 arcsec of an handful of objects with radio or X-ray cores. OB-stars are the dominant source of photoionization in 10 per cent of the <SMALL>SAURON</SMALL> sample, whereas for another 10 per cent the intense and highly ionized emission is powered by the pAGB population associated to a recently formed stellar subcomponent. Fast shocks are not an important source of ionization for the diffuse nebular emission of early-type galaxies since the required shock velocities can hardly be attained in the potential of our sample galaxies. Finally, in the most massive and slowly or non-rotating galaxies in our sample, which can retain a massive X-ray halo, the finding of a spatial correlation between the hot and warm phases of the interstellar medium (ISM) suggests that the interaction with the hot ISM provides an additional source of ionization besides old ultraviolet-bright stars. This is also supported by a distinct pattern towards lower values of the [O <SMALL>III</SMALL>]/Hβ ratio. These results lead us to investigate the relative role of stellar and AGN photoionization in explaining the ionized gas emission observed in early-type galaxies by the Sloan Digital Sky Survey (SDSS). By simulating how our sample galaxies would appear if placed at further distance and targeted by the SDSS, we conclude that only in very few, if any, of the SDSS galaxies which display modest values for the equivalent width of the [O <SMALL>III</SMALL>] line (less than ∼2.4 Å) and low-ionization nuclear emission-line region like [O <SMALL>III</SMALL>]/Hβ values the nebular emission is truly powered by an AGN.</P>
Improved spectral line measurements of the SDSS galaxy spectra
Oh, Kyu-Seok,Sarzi, Marc,Yi, Suk-Young 한국우주과학회 2009 한국우주과학회보 Vol.18 No.2
We have established a database of galaxy spectral line strengths for the SDSS database using an improved line measuring method. Our work includes the entire SDSS DR7 galaxies within redshift of 0.2. The absorption line strengths measured by the SDSS pipel
Galaxy Zoo: a sample of blue early-type galaxies at low redshift<sup>★</sup>
Schawinski, Kevin,Lintott, Chris,Thomas, Daniel,Sarzi, Marc,Andreescu, Dan,Bamford, Steven P.,Kaviraj, Sugata,Khochfar, Sadegh,Land, Kate,Murray, Phil,Nichol, Robert C.,Raddick, M. Jordan,Slosar, An Blackwell Publishing Ltd 2009 Monthly notices of the Royal Astronomical Society Vol.396 No.2
<P>ABSTRACT</P><P>We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5 < SFR < 50 M<SUB>⊙</SUB> yr<SUP>−1</SUP>). They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital Sky Survey Data Release 6 and their <I>u</I>−<I>r</I> colour. We select a volume-limited sample in the redshift range 0.02 < <I>z</I> < 0.05, corresponding to luminosities of approximately <I>L</I>* and above and with <I>u</I>−<I>r</I> colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties. Blue early-type galaxies tend to live in lower density environments than ‘normal’ red sequence early-types and make up 5.7 ± 0.4 per cent of the low-redshift early-type galaxy population. We find that such blue early-type galaxies are virtually absent at high velocity dispersions above 200 km s<SUP>−1</SUP>. Our analysis uses emission line diagnostic diagrams and we find that ∼25 per cent of them are actively star forming, while another ∼25 per cent host both star formation and an active galactic nucleus (AGN). Another ∼12 per cent are AGN. The remaining 38 per cent show no strong emission lines. When present and uncontaminated by an AGN contribution, the star formation is generally intense. We consider star formation rates derived from Hα, <I>u</I> band and infrared luminosities, and radial colour profiles, and conclude that the star formation is spatially extended. Of those objects that are not currently undergoing star formation must have ceased doing so recently in order to account for their blue optical colours. The gas-phase metallicity of the actively star-forming blue early-types galaxies is supersolar in all cases. We discuss the place of these objects in the context of galaxy formation. A catalogue of all 204 blue early-type galaxies in our sample, including star formation rates, emission line classification is provided.</P>
DESTRUCTION OF MOLECULAR GAS RESERVOIRS IN EARLY-TYPE GALAXIES BY ACTIVE GALACTIC NUCLEUS FEEDBACK
Schawinski, Kevin,Lintott, Chris J.,Thomas, Daniel,Kaviraj, Sugata,Viti, Serena,Silk, Joseph,Maraston, Claudia,Sarzi, Marc,Yi, Sukyoung K.,Joo, Seok-Joo,Daddi, Emanuele,Bayet, Estelle,Bell, Tom,Zuntz, IOP Publishing 2009 The Astrophysical journal Vol.690 No.2