Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821 (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2004
We present the stellar kinematics of 48 representative elliptical and lenticular galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data were homogeneously processed through a dedicated reduction and analysis pipeline. All resulting SAURON data cubes were spatially binned to a constant minimum signal-to-noise ratio. We have measured the stellar kinematics with an optimized (penalized pixel-fitting) routine which fits the spectra in pixel space, via the use of optimal templates, and prevents the presence of emission lines to affect the measurements. We have thus generated maps of the mean stellar velocity V, the velocity dispersion σ , and the Gauss-Hermite moments h 3 and h 4 of the line-of-sight velocity distributions. The maps extend to approximately one effective radius. Many objects display kinematic twists, kinematically decoupled components, central stellar discs, and other peculiarities, the nature of which will be discussed in future papers of this series.
Monthly Notices of the Royal Astronomical Society, 2006
We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O III]/Hβ ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954.
Monthly Notices of the Royal Astronomical Society, 2006
We present the emission-line fluxes and kinematics of 48 representative elliptical and lenticular galaxies obtained with our custom-built integral-field spectrograph, SAURON, operating on the William Herschel Telescope. Hβ, [O III]λλ4959,5007 and [N I] λλ5198,5200 emission lines were measured using a new procedure that simultaneously fits both the stellar spectrum and the emission lines. Using this technique we can detect emission lines down to an equivalent width of 0.1 Å set by the current limitations in describing galaxy spectra with synthetic and real stellar templates, rather than by the quality of our spectra. Gas velocities and velocity dispersions are typically accurate to within 14 and 20 km s −1 , respectively, and at worse to within 25 and 40 km s −1 . The errors on the flux of the [O III] and Hβ lines are on average 10 and 20 per cent, respectively, and never exceed 30 per cent. Emission is clearly detected in 75 per cent of our sample galaxies, and comes in a variety of resolved spatial distributions and kinematic behaviours. A mild dependence on the Hubble type and galactic environment is observed, with higher detection rates in lenticular galaxies and field objects. More significant is the fact that only 55 per cent of the galaxies in the Virgo cluster exhibit clearly detected emission. The ionized-gas kinematics is rarely consistent with simple coplanar circular motions. However, the gas almost never displays completely irregular kinematics, generally showing coherent motions with smooth variations in angular momentum. In the majority of the cases, the gas kinematics is decoupled from the stellar kinematics, and in half of the objects this decoupling implies a recent acquisition of gaseous material. Over the entire sample however, the distribution of the mean misalignment values between stellar and gaseous angular momenta is inconsistent with a purely external origin. The distribution of kinematic misalignment values is found to be strongly dependent on the apparent flattening and the level of rotational support of galaxies, with flatter, fast rotating objects hosting preferentially corotating gaseous and stellar systems. In a third of the cases, the distribution and kinematics of the gas underscore the presence of nonaxisymmetric perturbations of the gravitational potential. Consistent with previous studies, the presence of dust features is always accompanied by gas emission while the converse is not always true. A considerable range of values for the [O III]/Hβ ratio is found both across the sample and within single galaxies. Despite the limitations of this ratio as an emission-line diagnostic, this finding suggests either that a variety of mechanisms is responsible for the gas excitation in E and S0 galaxies or that the metallicity of the interstellar material is quite heterogeneous.
SAURON: Integral-field Spectroscopy of Galaxies
1999
We present the first results from a new and unique integral-field spectrograph, SAURON. Based upon the TIGER concept, SAURON uses a lens array to obtain two-dimensional spectroscopy with complete spatial coverage over a field of 33"x41" in low-resolution mode (0.94" lenslets) and of 9"x11" in high-resolution mode (0.26" lenslets). The spectra cover the wavelengths from 4800A to 5400A with a spectral resolution of ~3A (sigma~75 km/s. SAURON achieved first light during commissioning on the William Herschel Telescope on 1 February 1999. We are now commencing a systematic survey of the velocity dispersions, velocity fields, and line-strength distributions of nearby ellipticals and spiral bulges. The wide field of SAURON will be crucial for unraveling complicated velocity structures. In combination with available long-slit spectroscopy of the outer regions of the galaxies, HST spectra of the nuclei, HST imaging, and dynamical modeling, we will constrain the intrinsic shapes, mass-to-light ratios, and stellar populations in spheroids.
Monthly Notices of the Royal Astronomical Society, 2010
We present a stellar population analysis of the absorption line strength maps for 48 earlytype 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-tonoise, together with predictions from up-to-date stellar population models, we estimate the simple stellar population-equivalent (SSP-equivalent) age, metallicity and abundance ratio [α/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 SSPequivalent age, metallicity and abundance ratio [α/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 fieldof-view, and sometimes even showing signs of residual star-formation, are restricted to low mass systems (σ e 100 km s −1 or ∼2 ×10 10 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 disk/ring, also seen in the near-UV or mid-IR on top of an older underlying stellar population.
New Astronomy Reviews, 2006
We summarise the results and achievements of integral-field spectroscopy of early-type galaxies, observed as part of a survey using both the SAURON and OASIS spectrographs. From the perspective of integral-field spectroscopy, these otherwise smooth and featureless objects show a wealth of structure, both in their stellar kinematics and populations. We focus on the stellar content, and examine properties on both kiloparsec scales with SAURON, and scales of 100Õs of parsecs with OASIS. These complementary studies reveal two types of kinematically distinct components (KDCs), differing primarily in their intrinsic sizes. In previous studies, KDCs and their host galaxies have generally been found to be unremarkable in other aspects. We show that large KDCs, typical of the well-studied cases, indeed show little or no age differences with their host galaxy. The KDCs detected with the higher spatialresolution of OASIS are intrinsically smaller and include, in contrast, a significant fraction of young stars. We speculate on the relationship between KDCs and their host galaxies, and the implications for young populations in early-type galaxies.
Absorption-line strengths of 18 late-type spiral galaxies observed with SAURON
Monthly Notices of the Royal Astronomical Society, 2007
We present absorption line-strength maps for a sample of 18 Sb-Sd galaxies observed using the integral-field spectrograph SAURON operating at the William Herschel Telescope on La Palma, as part of a project devoted to the investigation of the kinematics and stellar populations of late-type spirals, a relatively unexplored field. The SAURON spectral range allows the measurement of the Lick/IDS indices Hβ, Fe5015 and Mgb, which can be used to estimate the stellar population parameters. We present here the two-dimensional line-strength maps for each galaxy. From the maps, we learn that late-type spiral galaxies tend to have high Hβ and low Fe5015 and Mgb values, and that the Hβ index has often a positive gradient over the field, while the metal indices peak in the central region. We investigate the relations between the central line-strength indices and their correlations with morphological type and central velocity dispersion, and compare the observed behaviour with that for ellipticals, lenticulars and early-type spirals from the SAURON survey. We find that our galaxies lie below the Mg -σ relation determined for elliptical galaxies and that the indices show a clear trend with morphological type. From the line-strength maps we calculate age, metallicity and abundance ratio maps via a comparison with model predictions; we discuss the results from a one-SSP (Single Stellar Population) approach and from a two-SSP approach, considering the galaxy as a superposition of an old (≈ 13 Gyr) and a younger (age 5 Gyr) population. We confirm that late-type galaxies are generally younger and more metal poor than ellipticals and have abundance ratios closer to solar values. We also explore a continuous star formation scenario, and try to recover the star formation history using the evolutionary models of , assuming constant or exponentially declining star formation rate (SFR). In this last case, fixing the galaxy age to 10 Gyr, we find a correlation between the e-folding time-scale τ of the starburst and the central velocity dispersion, in the sense that more massive galaxies tend to have shorter τ , suggesting that the star formation happened long ago and has now basically ended, while for smaller objects with larger values of τ it is still active now.
Kinematics and stellar populations in active galaxies: the LINER NGC 4579 (M58)
Astronomy & Astrophysics - ASTRON ASTROPHYS, 1997
We present long slit spectroscopy from the blue to the near-IR of the LINER galaxy NGC 4579 (M58). Stellar indices are used as tools to investigate if any differences in the kinematics and/or stellar content exist between the nucleus and the circumnuclear regions of the galaxy. Blue indices are found to be affected by contamination due to emission lines in the central region and the method to measure these indices is discussed. No peculiarities are found in the stellar kinematics with respect to the bulges of normal spirals, whose old population can fit the observations of the bulge of NGC 4579. Alternatively, the low central values of Mg_2_ and the high values of Mg_1_ in the blue and MgI in the near-IR lead us to propose the dominant bulge stellar population in NGC 4579 to be substantially younger than the one present in ordinary ellipticals and S0 galaxies, and therefore a population with an age of about (2.5+/-1)Gyr. and a metallicity of (1.5+/-0.5)Zsun_ is also able to reproduc...