Martin Bureau

Abstract:

We analyse the morphological structures in galaxies of the ATLAS3D sample by fitting a single Sérsic profile and decomposing all non-barred objects (180 of 260 objects) in two components parametrized by an exponential and a general Sérsic function. The aim of this analysis is to look for signatures of discs in light distributions of nearby early-type galaxies and compare them to kinematic properties. Using Sérsic index from single-component fits for a distinction between slow and fast rotators, or even late- and early-type galaxies, is not recommended. Assuming that objects with n > 3 are slow rotators (or ellipticals), there is only a 22 per cent probability to correctly classify objects as slow rotators (or 37 per cent of previously classified as ellipticals). We show that exponential sub-components, as well as light profiles fitted with only a single component of a low Sérsic index, can be linked with the kinematic evidence for discs in early-type galaxies. The median disc-to-total light ratio for fast and slow rotators is 0.41 and 0.0, respectively. Similarly, the median Sérsic indices of the bulge (general Sérsic component) are 1.7 and 4.8 for fast and slow rotators, respectively. Overall, discs or disc-like structures are present in 83 per cent of early-type galaxies which do not have bars, and they show a full range of disc-to-total light ratios. Discs in early-type galaxies contribute with about 40 per cent to the total mass of the analysed (non-barred) objects. The decomposition into discs and bulges can be used as a rough approximation for the separation between fast and slow rotators, but it is not a substitute, as there is only a 59 per cent probability to correctly recognize slow rotators. We find trends between the angular momentum and the disc-to-total light ratios and the Sérsic index of the bulge, in the sense that high angular momentum galaxies have large disc-to-total light ratios and small bulge indices, but there is none between the angular momentum and the global Sérsic index. We investigate the inclination effects on the decomposition results and confirm that strong exponential profiles can be distinguished even at low inclinations, but medium-size discs are difficult to quantify using photometry alone at inclinations lower than ∼50°. Kinematics (i.e. projected angular momentum) remains the best approach to mitigate the influence of the inclination effects.We also find weak trends with mass and environmental density, where disc-dominated galaxies are typically less massive and found at all densities, including the densest region sampled by the ATLAS3D sample. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

For early-type galaxies, the ability to sustain a corona of hot, X-ray-emitting gas could have played a key role in quenching their star formation history. A halo of hot gas may act as an effective shield against the acquisition of cold gas and can quickly absorb stellar mass loss material. Yet, since the discovery by the Einstein Observatory of such X-ray haloes around early-type galaxies, the precise amount of hot gas around these galaxies still remains a matter of debate. By combining homogeneously derived photometric and spectroscopic measurements for the early-type galaxies observed as part of the ATLAS3D integral field survey with measurements of their X-ray luminosity based on X-ray data of both low and high spatial resolution (for 47 and 19 objects, respectively) we conclude that the hot gas content of early-type galaxies can depend on their dynamical structure. Specifically, whereas slow rotators generally have X-ray haloes with luminosity LX, gas and temperature T values that are well in line with what is expected if the hot gas emission is sustained by the thermalization of the kinetic energy carried by the stellar mass loss material, fast rotators tend to display LX, gas values that fall consistently below the prediction of thismodel, with similar T values that do not scale with the stellar kinetic energy (traced by the stellar velocity dispersion) as observed in the case of slow rotators. Such a discrepancy between the hot gas content of slow and fast rotators would appear to reduce, or even disappear, for large values of the dynamical mass (above ∼3× 1011Mȯ), with younger fast rotators displaying also somewhat larger LX, gas values possibly owing to the additional energy input from recent supernovae explosions. Considering that fast rotators are likely to be intrinsically flatter than slow rotators, and that the few LX, gas-deficient slow rotators also happen to be relatively flat, the observed LX, gas deficiency in these objects would support the hypothesis whereby flatter galaxies have a harder time in retaining their hot gas, although we suggest that the degree of rotational support could further hamper the efficiency with which the kinetic energy of the stellar mass loss material is thermalized in the hot gas. We discuss the implications that a different hot gas content could have on the fate of both acquired and internally produced gaseous material, considering in particular how the LX, gas deficiency of fast rotators would make them more capable to recycle the stellar mass loss material into new stars than slow rotators. This would be consistent with the finding that molecular gas and young stellar populations are detected only in fast rotators across the entire ATLAS3D sample, and that fast rotators tend to have a larger specific dust mass content than slow rotators. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

In the companion Paper XV of this series, we derive accurate total mass-to-light ratios (M/L)JAM ≈ (M/L)(r = Re) within a sphere of radius r = Re centred on the galaxy, as well as stellar (M/L)stars (with the dark matter removed) for the volume-limited and nearly massselected (stellarmassM* ≲ 6 × 109M⊙)ATLAS3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). Here, we use those parameters to study the two orthogonal projections (MJAM, σe) and (MJAM,R maje ) of the thin Mass Plane (MP) (MJAM, σe,Rmaje ) which describes the distribution of the galaxy population, where MJAM = L × (M/L)JAM ≈ M*. The distribution of galaxy properties on both projections of the MP is characterized by: (i) the same zone of exclusion (ZOE), which can be transformed from one projection to the other using the scalar virial equation. The ZOE is roughly described by two power laws, joined by a break at a characteristic mass MJAM ≈ 3 × 1010M⊙, which corresponds to the minimum Re and maximum stellar density. This results in a break in the meanMJAM-σe relation with trends MJAM α σ2.3e and MJAM α σ4.7e at small and large σe, respectively; (ii) a characteristic mass MJAM ≈ 2 × 1011M⊙ which separates a population dominated by flat fast rotator with discs and spiral galaxies at lower masses, from one dominated by quite round slow rotators at larger masses; (iii) below that mass the distribution of ETGs' properties on the two projections of the MP tends to be constant along lines of roughly constant se, or equivalently along lines with Rmaje α MJAM, respectively (or even better parallel to the ZOE: Rmaje α M0.75JAM); (iv) it forms a continuous and parallel sequence with the distribution of spiral galaxies; (v) at even lower masses, the distribution of fast-rotator ETGs and late spirals naturally extends to that of dwarf ETGs (Sph) and dwarf irregulars (Im), respectively. We use dynamical models to analyse our kinematic maps. We show that σe traces the bulge fraction, which appears to be the main driver for the observed trends in the dynamical (M/L)JAM and in indicators of the (M/L)pop of the stellar population like Hβ and colour, as well as in the molecular gas fraction. A similar variation along contours of σe is also observed for the mass normalization of the stellar initial mass function (IMF), which was recently shown to vary systematically within the ETGs' population. Our preferred relation has the form log10[(M/L)stars/(M/L)Salp] = a + b × log10(σe/130 km s-1) with a=-0.12 ± 0.01 and b = 0.35 ± 0.06. Unless there are major flaws in all stellar population models, this trend implies a transition of the mean IMF from Kroupa to Salpeter in the interval log10(σe/km s-1) ≈ 1.9-2.5 (or σe ≈ 90-290 km s-1), with a smooth variation in between, consistently with what was shown in Cappellari et al. The observed distribution of galaxy properties on the MP provides a clean and novel view for a number of previously reported trends, which constitute special two-dimensional projections of the more general four-dimensional parameters trends on the MP. We interpret it as due to a combination of two main effects: (i) an increase of the bulge fraction, which increases σe, decreases Re, and greatly enhance the likelihood for a galaxy to have its star formation quenched, and (ii) dry merging, increasing galaxy mass and Re by moving galaxies along lines of roughly constant σe (or steeper), while leaving the population nearly unchanged. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We investigate nuclear light profiles in 135 ATLAS3D galaxies for which the Hubble Space Telescope (HST) imaging is available and compare them to the large-scale kinematics obtained with the SAURONintegral-field spectrograph. Specific angular momentum, λR, correlateswith the shape of nuclear light profiles, where, as suggested by previous studies, cores are typically found in slow rotators and core-less galaxies are fast rotators. As also shown before, cores are found only in massive galaxies and only in systems with the stellar mass (measured via dynamical models) M ≳ 8 × 1010 M· Based on our sample, we, however, see no evidence for a bimodal distribution of nuclear slopes. The best predictor for finding a core is based on the stellar velocity dispersion within an effective radius, se, and specific angular momentum, where cores are found for λR ≲ 0.25 and σe ≳ 160 kms-1. We estimate that only about 10 per cent of nearby early-type galaxies contain cores. Furthermore, we show that there is a genuine population of fast rotators with cores. We also show that core fast rotators are morphologically, kinematically and dynamically different from core slow rotators. The cores of fast rotators, however, could harbour black holes of similar masses to those in core slow rotators, but typically more massive than those found in core-less fast rotators. Cores of both fast and slow rotators are made of old stars and found in galaxies typically lacking molecular or atomic gas (with a few exceptions). Core-less galaxies, and especially core-less fast rotators, are underluminous in the diffuse X-ray emission, but the presence of a core does not imply high X-ray luminosities. Additionally, we postulate (as many of these galaxies lack HST imaging) a possible population of core-less galaxies among slow rotators, which cannot be explained as face-on discs, but comprise a genuine sub-population of slow rotators. These galaxies are typically less massive and flatter than core slow rotators, and show evidence for dynamical cold structures and exponential photometric components. Based on our findings, major nondissipative (gas-poor) mergers together with black hole binary evolution may not be the only path for formation of cores in early-type galaxies. We discuss possible processes for formation of cores and their subsequent preservation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.