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Abstract:

We present a stellar population analysis of the absorption line strength maps for 48 early-type galaxies from the SAURON sample. Using the line strength index maps of Hβ, Fe5015 and Mg b, measured in the Lick/IDS system and spatially binned to a constant signal-to-noise ratio, together with predictions from up-to-date stellar population models, we estimate the simple stellar population-equivalent (SSP-equivalent) age, metallicity and abundance ratio [alpha;/Fe] over a two-dimensional field extending up to approximately one effective radius. A discussion of calibrations and differences between model predictions is given. Maps of SSP-equivalent age, metallicity and abundance ratio [alpha;/Fe] are presented for each galaxy. We find a large range of SSP-equivalent ages in our sample, of which ~40 per cent of the galaxies show signs of a contribution from a young stellar population. The most extreme cases of post-starburst galaxies, with SSP-equivalent ages of ≤3 Gyr observed over the full field-of-view, and sometimes even showing signs of residual star formation, are restricted to low-mass systems (σe≤ 100 km s^-1 or ~2 × 10¹⁰ M.). Spatially restricted cases of young stellar populations in circumnuclear regions can almost exclusively be linked to the presence of star formation in a thin, dusty disc/ring, also seen in the near-UV or mid-IR on top of an older underlying stellar population.The flattened components with disc-like kinematics previously identified in all fast rotators are shown to be connected to regions of distinct stellar populations. These range from the young, still star-forming circumnuclear discs and rings with increased metallicity preferentially found in intermediate-mass fast rotators, to apparently old structures with extended disc-like kinematics, which are observed to have an increased metallicity and mildly depressed [alpha;/Fe] ratio compared to the main body of the galaxy. The slow rotators, often harbouring kinematically decoupled components (KDC) in their central regions, generally show no stellar population signatures over and above the well-known metallicity gradients in early-type galaxies and are largely consistent with old (≥10 Gyr) stellar populations.Using radially averaged stellar population gradients we find in agreement with Spolaor et al. a mass-metallicity gradient relation where low-mass fast rotators form a sequence of increasing metallicity gradient with increasing mass. For more massive systems (above ~3.5 × 10¹⁰ M.) there is an overall downturn such that metallicity gradients become shallower with increased scatter at a given mass leading to the most massive systems being slow rotators with relatively shallow metallicity gradients. The observed shallower metallicity gradients and increased scatter could be a consequence of the competition between different star formation and assembly scenarios following a general trend of diminishing gas fractions and more equal-mass mergers with increasing mass, leading to the most massive systems being devoid of ordered motion and signs of recent star formation. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

We demonstrate that the comparison of Tully-Fisher relations (TFRs) derived from global H-i linewidths to TFRs derived from the circular-velocity profiles of dynamical models (or stellar kinematic observations corrected for asymmetric drift) is vulnerable to systematic and uncertain biases introduced by the different measures of rotation used. We therefore argue that to constrain the relative locations of the TFRs of spiral and S0 galaxies, the same tracer and measure must be used for both samples. Using detailed near-infrared imaging and the circular velocities of axisymmetric Jeans models of 14 nearby edge-on Sa-Sb spirals and 14 nearby edge-on S0s drawn from a range of environments, we find that S0s lie on a TFR with the same slope as the spirals, but are on average 0.53 ± 0.15-mag fainter at KS band at a given rotational velocity. This is a significantly smaller offset than that measured in earlier studies of the S0 TFR, which we attribute to our elimination of the bias associated with using different rotation measures and our use of earlier-type spirals as a reference. Since our measurement of the offset avoids systematic biases, it should be preferred to previous estimates. A spiral stellar population in which star formation is truncated would take ≈1-Gyr to fade by 0.53-mag at KS band. If S0s are the products of a simple truncation of star formation in spirals, then this finding is difficult to reconcile with the observed evolution of the spiral/S0 fraction with redshift. Recent star formation could explain the observed lack of fading in S0s, but the offset of the S0 TFR persists as a function of both stellar and dynamical mass. We show that the offset of the S0 TFR could therefore be explained by a systematic difference between the total mass distributions of S0s and spirals, in the sense that S0s need to be smaller or more concentrated than spirals. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

The clustering properties of a well-defined sample of 734 ±áα emitters at z= 0.845 ± 0.015, obtained as part of the Hi-z Emission Line Survey, are investigated. The spatial correlation function of these ±áα emitters is very well described by the power-law ξ = (r/r0)^-1.8, with a real-space correlation, r0, of 2.7 ± 0.3 h^-1 Mpc. The correlation length r0 increases strongly with ±áα luminosity (L±áα), from r0 ∼ 2 h^-1 Mpc for the most quiescent galaxies [star formation rates (SFRs) of ∼4 M⊙ yr^-1] up to r0 > 5 h^-1 Mpc for the brightest galaxies in ±áα. The correlation length also increases with increasing rest-frame K-band (MK) luminosity, but the r0-L±áα correlation maintains its full statistical significance at fixed MK. At z = 0.84, star-forming galaxies classified as irregulars or mergers are much more clustered than discs and non-mergers, respectively; however, once the samples are matched in L±áα and MK, the differences vanish, implying that the clustering is independent of morphological type at z ∼ 1 just as in the local Universe. The typical ±áα emitters found at z = 0.84 reside in dark matter haloes of ≈10¹² M⊙, but those with the highest SFRs reside in more massive haloes of ≈10¹³ M⊙. The results are compared with those of ±áα surveys at different redshifts: although the break of the ±áα luminosity function L*±áα evolves by a factor of ∼30 from z= 0.24 to 2.23, if the ±áα luminosities at each redshift are scaled by L*±áα(z) then the correlation lengths indicate that, independently of cosmic time, galaxies with the same (L±áα)/L*±áα(z) are found in dark matter haloes of similar masses. This not only confirms that the star formation efficiency in high redshift haloes is higher than locally but also suggests a fundamental connection between the strong negative evolution of L*±áα since z = 2.23 and the quenching of star formation in galaxies residing within dark matter haloes significantly more massive than 10¹² M⊙ at any given epoch. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg ² of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands. © 2010. The Astronomical Society of the Pacific. All rights reserved.