Spatially resolved spectroscopy of early-type galaxies over a range in mass

By P. Sánchez-Blázquez, D. Forbes, J. Strader, J. Brodie, Robert N. Proctor. 2007

133 citations recorded by the source corpus.

Long-slit spectra have been obtained with the Keck telescope for a sample of 11 early-type galaxies covering a wide range in luminosity and hence mass. Rotation velocity and velocity dispersions, together with 19 Lick line-strength gradients have been measured, to, on average, two effective radii. Stellar population models taking into account the effect of the non-solar chemical composition have been used to derive ages, metallicities and α/Fe abundances along the radius. We find that line-strength gradients are due mainly to variations of the total metallicity with the radius. One galaxy out of 11 shows very strong age gradients, with a young central component, while the age gradient for the rest of the sample is very shallow or consistent with zero. We also find small variations in the [c /Fe] ratio with radius. Contrary to what is expected in simple collapse models, galaxies show both positive and negative [α/Fe] profiles. This rules out a solely inside-out, or outside-in, formation mechanism for all early-type galaxies. We do not find a correlation between the metallicity and the [a/Fe] gradients, and the local metallicity is not correlated with the local velocity dispersion for all the galaxies of our sample, which rules out scenarios where the delay in the onset of the galactic winds is the only mechanism producing the metallicity gradients. We found that metallicity gradients are correlated with the shape of the isophotes and the central mean age and metallicity of the galaxies, for galaxies younger than ∼10 Gyr. We show that the correlation between the gradients and the central values is not due to the correlation of the errors and indicates that the same process that shaped the gradient, also modified the structural parameters of the galaxies and triggered star formation in their centres. This strongly supports the merger scenario for the formation of these systems, where the degree of dissipation during those mergers increases as the mass of the progenitor galaxies decreases. Finally, we also find a dichotomy in the plane grad [a/Fe]-[a/Fe] between galaxies with velocity dispersions below and above ∼200 km s -1 , which requires confirmation with larger samples.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ae0c4fb9f7c382dd6884c2e21e15e2605441b631

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Citations in the corpus

Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “…1992; Sanders & Mirabel 1996; Titus, Spillar & Johnson 1997; Hibbard & Yun 1999; Reichardt, Jimenez & Heavens 2001; Tacconi et al. 2002; Rothberg & Joseph 2004; Michard 2006; Sánchez-Blázquez et al. 2007; Foster et al. 2009; Kewley et al. 2010; Rupke, Kewley & Barnes 2010; Soto & Martin 2010).”
Compact high-redshift galaxies are the cores of the most massive present-day spheroids (2009, background): “Some efforts have been made along these lines (see e.g. Sánchez-Blázquez et al. 2007), and gradients in e.g. α-element abundances show significant diversity, suggesting that in some systems, envelopes formed quickly (perhaps in e.g. later-forming ellipticals, where a large envelope can be formed…”
Discriminating Between the Physical Processes that Drive Spheroid Size Evolution (2009, background): “…material at the centre) yielding a slightly red core (typical in z = 0 massive ellipticals; see Caon, Capaccioli & Rampazzo 1990; Peletier et al. 1990; Kuntschner et al. 2006; Sánchez-Blázquez et al. 2007), the B-band Re here is about ∼10 per cent larger than the stellar mass Re at late times.”
The star formation history of CALIFA galaxies: Radial structures (2013, background): “Spectroscopic data and measured line-strength stellar indices can help to break these degeneracies (Trager et al. 2000; Proctor & Sansom 2002; Sánchez-Blázquez et al. 2007; MacArthur et al. 2009).”
The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, result): “Independent tests (Balcells, Graham & Peletier 2007a; Hopkins et al. 2008b; Kormendy et al. 2009) and constraints from stellar populations (McDermid et al. 2006; Reda et al. 2007; Sánchez-Blázquez et al. 2007) yield similar conclusions.”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. II. “CUSP” ELLIPTICALS (2008, methodology): “We consider the elliptical NGC 3377, for which detailed stellar population gradients have been measured by Sánchez-Blázquez et al. (2007).”
Evolutionary stellar population synthesis with MILES – I. The base models and a new line index system (2010, methodology): “We plot the radial line-strength profile for the Virgo galaxy NGC4387, which has been obtained from low resolution Keck/LRIS spectra by Sánchez-Blázquez et al. (2007).”
The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies (2010, background): “Only a limited number of studies have investigated line strength gradients obtained with long slits (e.g., Davies et al. 1993; Sánchez-Blázquez et al. 2007; Spolaor et al. 2009) or radially averaging the data from integral-field-units (Rawle et al. 2008); spatially resolved stellar population…”