Showing papers by "Jesús Falcón-Barroso published in 2007"

The SAURON project – IX. A kinematic classification for early‐type galaxies

Abstract: Two-dimensional stellar kinematics of 48 representative elliptical (E) and lenticular (S0) galaxies obtained with the SAURON integral-field spectrograph reveal that early-type galaxies appear in two broad flavours, depending on whether they exhibit clear large-scale rotation or not. We define a new parameter lambda(R) equivalent to / , which involves luminosity-weighted averages over the full two-dimensional kinematic field as a proxy to quantify the observed projected stellar angular momentum per unit mass. We use it as a basis for a new kinematic classification: early-type galaxies are separated into slow and fast rotators, depending on whether they have lambda(R) values within their effective radius R(e) below or above 0.1, respectively. Slow and fast rotators are shown to be physically distinct classes of galaxies, a result which cannot simply be the consequence of a biased viewing angle. Fast rotators tend to be relatively low-luminosity galaxies with M(B) greater than or similar to-20.5. Slow rotators tend to be brighter and more massive galaxies, but are still spread over a wide range of absolute magnitude. Three slow rotators of our sample, among the most massive ones, are consistent with zero rotation. Remarkably, all other slow rotators (besides the atypical case of NGC 4550) contain a large kpc-scale kinematically decoupled core (KDC). All fast rotators (except one galaxy with well-known irregular shells) show well-aligned photometric and kinemetric axes, and small velocity twists, in contrast with most slow rotators which exhibit significant misalignments and velocity twists. These results are supported by a supplement of 18 additional early-type galaxies observed with SAURON. In a companion paper (Paper X), we also show that fast and slow rotators are distinct classes in terms of their orbital distribution. We suggest that gas is a key ingredient in the formation and evolution of fast rotators, and that the slowest rotators are the extreme evolutionary end point reached deep in gravitational potential wells where dissipationless mergers had a major role in the evolution, and for which most of the baryonic angular momentum was expelled outwards. Detailed numerical simulations in a cosmological context are required to understand how to form large-scale KDCs within slow rotators, and more generally to explain the distribution of lambda(R) values within early-type galaxies and the distinction between fast and slow rotators.

The SAURON project – X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/σ, ɛ) diagram with integral‐field stellar kinematics

Abstract: We analyse the orbital distribution of elliptical (E) and lenticular (S0) galaxies using SAURON integral-field stellar kinematics within about one effective (half-light) radius. We construct the anisotropy diagram, which relates the ratio of the ordered and random motion in a galaxy (V/sigma) to its observed ellipticity (epsilon), for the 48 E/S0 galaxies from the SAURON survey. For a subsample of 24 galaxies consistent with axisymmetry, we use three-integral axisymmetric Schwarzschild dynamical models to recover the detailed orbital distribution, and we find good agreement with the anisotropy derived from the (V/sigma, epsilon) diagram. In a companion paper (Paper IX), we show that the early-type galaxies can be subdivided into two classes of systems with or without a significant amount of specific stellar angular momentum. Here, we show that the two classes have different distributions on the (V/sigma, epsilon) diagram. The slow rotators are more common among the most massive systems and are generally classified as E from photometry alone. Those in our sample tend to be fairly round(epsilon less than or similar to 0.3), but can have significant kinematical misalignments, indicating that as a class they are moderately triaxial, and span a range of anisotropies (delta less than or similar to 0.3). The fast rotators are generally fainter and are classified as either E or S0. They can appear quite flattened (epsilon less than or similar to 0.7), do not show significant kinematical misalignments (unless barred or interacting), indicating they are nearly axisymmetric and span an even larger range of anisotropies (delta less than or similar to 0.5). These results are confirmed when we extend our analysis to 18 additional E/S0 galaxies observed with SAURON. The dynamical models indicate that the anisotropy inferred from the (V/sigma, epsilon) diagram is due to a flattening of the velocity ellipsoid in the meridional plane (sigma(R) > sigma(z)), which we quantify with the beta anisotropy parameter. We find a trend of increasing beta for intrinsically flatter galaxies. A number of the fast rotators show evidence for containing a flattened, kinematically distinct component, which in some cases counter-rotates relative to the main galaxy body. These components are generally more metal rich than the galaxy body. All these results support the idea that fast rotators are nearly oblate and contain disc-like components. The role of gas must have been important for their formation. The slow rotators are weakly triaxial. Current collisionless merger models seem unable to explain their detailed observed properties.

Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters

Abstract: We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for MILES, a new spectral stellar library covering the range lambda lambda 3525-7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.

The SAURON project - XI. Stellar Populations from Absorption Line Strength Maps of 24 Early-Type Spirals

Abstract: We present absorption line strength maps of a sample of 24 representative early-type spiral galaxies, mostly of type Sa, obtained as part of the SAURON survey of nearby galaxies using our custom-built integral-field spectrograph. Using high- quality spectra, spatially binned to a constant signal-to-noise, we measure several key age, metallicity and abundance ratio sensitive indices from the Lick/IDS system over a contiguous two-dimensional field including bulge and inner disc. We present maps of Hβ, Fe 5015, and Mgb, for each galaxy. We find that Sa galaxies on the average have slightly smaller Mg b and Fe 5015 line strengths than ellipticals and S0s, and higher Hβ values, but with a much larger scatter. The absorption line maps show that many galaxies contain some younger populations (6 1 Gyr), distributed in small or large inner discs, or in circu mnuclear star forming rings. In many cases these young stars are formed in circumnuclear mini-starbursts, which are dominating the light in the centres of some of the early-type spir als. These mini-starburst cause a considerable scatter in index-index diagrams such as Mg b ‐ Hβ and Mgb ‐ Fe 5015, more than is measured for early-type galaxies. We find that the cen tral regions of Sa galaxies display a wide range in ages, even within the galaxies. We find that the central regions of early-type spirals are often dusty, with a good correlation between the presence of young central stellar populations and a significant amount of dust extinction. 50% of the sample show velocity dispersion drops in their centres. All of the galaxies of our sample lie on or below the Mg b ‐ σ relation for elliptical galaxies in the Coma cluster, and above the Hβ absorption line ‐ σ relation for elliptical galaxies. If those relations are considered to be relations for the oldest local galaxies we see that our sample of spirals has a considerable scatter in age, with the largest scatter at the lowest σ. This is in disagreement with highly inclined samples, in which generally only old stellar populations are found in the central regions. The discrepancy between our sample and highly inclined samples, and the presence of so many stellar velocity dispersion dips, i.e., so-called σ-drops, in these spiral galaxies with large bulges (type Sa) can be understood if the central regions of Sa galaxies contain at least 2 components: a thin, disc-like component, often containing recent star formation, and another, elliptical-like component, consisting of old stars and rot ating more slowly, dominating the light above the plane. These components together form the photometrically defined bulge, in the same way as the thin and the thick disc co-exist in the solar neighbourhood. In this picture, consistent with the current literature, part of the bulge, t he thicker component, formed a very long time ago. Later, stars continued to form in the central r egions of the disc, rejuvenating in this way the bulge through dynamical processes. This picture is able to explain in a natural way the heterogeneous stellar populations and star formation characteristics that we are seeing in detailed observations of early-type spiral galaxies.

Absorption-line strengths of 18 late-type spiral galaxies observed with SAURON

Abstract: 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 H beta, 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 H beta and low Fe5015 and Mgb values, and that the H beta 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-sigma 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 (approximate to 13 Gyr) and a younger (age

Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics

Abstract: We study the two-dimensional kinematics of the Hα-emitting gas in the nearby barred Scd galaxy NGC 6946, in order to determine the pattern speed of the primary m = 2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and setting up an evolutionary scenario for NGC 6946. Our data allow us to derive the best-fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. We find a main pattern speed Ω = 22 km s-1 kpc-1, but our data clearly reveal the presence of an additional pattern speed Ω = 47 km s-1 kpc-1 in a zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we deduce the location of the resonance radii and confirm that inside the outer inner Lindblad resonance radius of the main oval, a primary bar has formed rotating at more than twice the outer pattern speed. We further confirm that a nuclear bar has formed inside the inner Lindblad resonance radius of the primary bar, coinciding with the inner inner Lindblad resonance radius of the large-scale m = 2 mode oval.

Absorption line-strengths of 18 late-type spiral galaxies observed with SAURON

Abstract: We present absorption line-strength maps for a sample of 18 Sb-Sd galaxies observed using the integral-field spectrograph SAURON. The SAURON spectral range allows the measurement of the Lick/IDS indices Hbeta, 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 Hbeta and low Fe5015 and Mgb values, and that the Hbeta 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 - sigma 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 and discuss the results from a one-SSP approach and from a two-SSP approach. 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 Bruzual & Charlot (2003), assuming constant or exponentially declining star formation rate (SFR). We find a correlation between the e-folding time-scale tau of the starburst and the central velocity dispersion: more massive galaxies tend to have shorter tau, suggesting that the star formation happened long ago and has now basically ended, while for smaller objects with larger values of tau it is still active.

A SINFONI view of Galaxy Centers: Morphology and Kinematics of five Nuclear Star Formation Rings

Abstract: We present near-infrared (H- and K-band) integral-field observations of the circumnuclear star formation rings in five nearby spiral galaxies. The data, obtained at the Very Large Telescope with the SINFONI spectrograph, are used to construct maps of various emission lines that reveal the individual star forming regions ("hot spots") delineating the rings. We derive the morphological parameters of the rings, and construct velocity fields of the stars and the emission line gas. We propose a qualitative, but robust, diagnostic for relative hot spot ages based on the intensity ratios of the emission lines Brackett gamma, HeI, and [FeII]. Application of this diagnostic to the data presented here provides tentative support for a scenario in which star formation in the rings is triggered predominantly at two well-defined regions close to, and downstream from, the intersection of dust lanes along the bar with the inner Lindblad resonance.

Supermassive black holes from OASIS and SAURON integral-field kinematics

Abstract: Supermassive black holes are a key element in our understanding of how galaxies form. Most of the progress in this very active field of research is based on just � 30 determi- nations of black hole mass, accumulated over the past decade. We illustrate how integral-field spectroscopy, and in particular our OASIS modeling effort, can help improve the current situation.

The SAURON project -- IX. A kinematic classification for early-type galaxies

Abstract: 2D stellar kinematics of 48 representative E and S0 galaxies obtained with the SAURON IFS reveal that early-type galaxies appear in two broad flavours, depending on whether they exhibit clear large-scale rotation or not. We define a new parameter LambdaR which involves luminosity weighted averages over the full 2D kinematic field, as a proxy to quantify the observed projected stellar angular momentum per unit mass. We use it as a basis for a new kinematic classification: early-type galaxies are separated into slow and fast rotators (SRs, FRs), depending on whether they have LambdaR values within their effective radius Re below or above 0.1, respectively. SRs and FRs are shown to be physically distinct classes of galaxies, a result which cannot simply be the consequence of a biased viewing angle. FRs tend to be relatively low luminosity galaxies. SRs tend to be brighter and more massive galaxies, but are still spread over a wide range of absolute magnitude. 3 slow rotators of our sample, among the most massive ones, are consistent with zero rotation. Remarkably, all other SRs contain a large kpc-scale KDC. All FRs show well aligned photometric and kinemetric axes, and small velocity twists, in contrast with most SRs which exhibit significant misalignments and velocity twists. In a companion paper (Paper X), we also show that FRs and SRs are distinct classes in terms of their orbital distribution. We suggest that gas is a key ingredient in the formation and evolution of FRs, and that the slowest rotators are the extreme evolutionary end point reached deep in gravitational potential wells where dissipationless mergers had a major role in the evolution, and for which most of the baryonic angular momentum was expelled outwards. (abridged)

Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics

Abstract: We study the two-dimensional kinematics of the H-alpha-emitting gas in the nearby barred Scd galaxy, NGC 6946, in order to determine the pattern speed of the primary m=2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and to set up an evolutionary scenario for NGC 6946. Our data allows us to derive the best fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. We find a main pattern speed Omega_p=22 km/s/kpc, but our data clearly reveal the presence of an additional pattern speed Omega_p=47 km/s/kpc in a zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we deduce the location of the resonance radii and confirm that inside the outer Inner Lindblad Resonance radius of the main oval, a primary bar has formed rotating at more than twice the outer pattern speed. We further confirm that a nuclear bar has formed inside the Inner Lindblad Resonance radius of the primary bar, coinciding with the inner Inner Lindblad Resonance radius of the large-scale m=2 mode oval.

A SINFONI view of circum-nuclear star-forming rings in spiral galaxies

Abstract: We present near-infrared (H- and K-band) SINFONI integral-field observations of the circumnuclear star formation rings in five nearby spiral galaxies. We made use of the relative intensities of different emission lines (i.e. [FeII], HeI, Brγ) to age date the stellar clusters present along the rings. This qualitative, yet robust, method allows us to discriminate between two distinct scenarios that describe how star formation progresses along the rings. Our findings favour a model where star formation is triggered predominantly at the intersection between the bar major axis and the inner Lindblad resonance and then passively evolves as the clusters rotate around the ring ( ‘Pearls on a string’ scenario), although models of stochastically distributed star formation ( ‘Popcorn’ model) cannot be completely ruled out.

Spiral galaxies in the SAURON survey

Abstract: . We discuss some recent integral field spectroscopy using the SAURON instrument of a sample consisting of 24 early-type spirals, part of the SAURON Survey, and 18 late-type spirals. Using 2-dimensional maps of their stellar radial velocity, velocity dispersion, and absorption line strength, it is now much easier to understand the nature of nearby galactic bulges. We discuss a few highlights of this work, and point out some new ideas about the formation of galactic bulges.

Star-Forming Nuclear Rings in Spiral Galaxies

Abstract: The study of gas transport to the inner regions of galaxies is a fundamental aspect in our understanding of the way galaxies evolve. In this context, starforming nuclear rings are key features as they contain large amounts of gas and are the sites where a significant fraction of the current star formation is taking place in their host galaxies. Here we present some results from a study of how star formation progresses along nuclear star-forming rings in five spiral galaxies, based on near-infrared SINFONI integral-field observations at the VLT.

Fast and Slow Rotators: The build-up of the Red Sequence

Abstract: Using the unique dataset obtained within the course of the SAURON project, a radically new view of the structure, dynamics and stellar populations of early-type galaxies has emerged We show that galaxies come in two broad flavours (slow and fast rotators), depending on whether or not they exhibit clear large-scale rotation, as indicated via a robust measure of the specific angular momentum of baryons This property is also linked with other physical characteristics of early-type galaxies, such as: the presence of dynamically decoupled cores, orbital structure and anisotropy, stellar populations and dark matter content I here report on the observed link between this baryonic angular momentum and a mass sequence, and how this uniquely relates to the building of the red sequence via dissipative/dissipationless mergers and secular evolution

The kinematics of Core and Cusp galaxies: comparing HST imaging and integral-field observations

Abstract: In this proceeding we look at the relationship between the photometric nuclear properties of early-type galaxies from Hubble Space Telescope imaging and their overall kinematics as observed with the SAURON integral-field spectrograph. We compare the inner slope of their photometric profiles and the Slow/Fast rotator classes, defined by the amplitude of a newly defined LambdaR parameter, to show that slow rotators tend to be more massive systems and display shallower inner profiles and fast rotators steper ones. It is important to remark, however, that there is not a one-to-one relationship between the two photometric and kinematic groups.

Fast and slow rotators: The build-up of the red sequence

Abstract: Using the unique dataset obtained within the course of the SAURON project, a radically new view of the structure, dynamics and stellar populations of early-type galaxies has emerged. We show that galaxies come in two broad flavours (slow and fast rotators), depending on whether or not they exhibit clear large-scale rotation, as indicated via a robust measure of the specific angular momentum of baryons. This property is also linked with other physical characteristics of early-type galaxies, such as: the presence of dynamically decoupled cores, orbital structure and anisotropy, stellar populations and dark matter content. I here report on the observed link between this baryonic angular momentum and a mass sequence, and how this uniquely relates to the building of the red sequence via dissipative/dissipationless mergers and secular evolution.

A sauron study of stars and gas in sa bulges

Abstract: We present results from our ongoing effort to understand the morphological and kinematical properties of early-type galaxies using the integral-field spectrograph SAURON. We discuss the relation between the stellar and gas morphology and kinematics in our sub-sample of 24 representative Sa spiral bulges. We focus on the frequency of kinematically decoupled components and on the presence of star formation in circumnuclear rings.

Stellar populations in late-type spirals observed with SAURON

Abstract: We present results on the stellar populations of a sample of 18 late-type spirals, based on data acquired with the integral-field spectrograph SAURON at the WHT. We present the two-dimensional line-strength maps, the central line indices, and estimate the star formation time-scale. In an exponentially declining SFR scenario, we find a trend between the time-scale τ and the central velocity dispersion: more massive galaxies show shorter burst durations. A detailed study on these data is published by Ganda et al. (2007).

The SAURON project - XI. Stellar Populations from Absorption Line Strength Maps of 24 Early-Type Spirals

Abstract: We present absorption line strength maps of a sample of 24 representative early-type spiral galaxies, mostly of type Sa, obtained as part of the SAURON survey of nearby galaxies using our custom-built integral-field spectrograph. Using high-quality spectra, spatially binned to a constant signal-to-noise, we measure several key age, metallicity and abundance ratio sensitive indices from the Lick/IDS system over a contiguous two-dimensional field including bulge and inner disc. We present maps of H beta, Fe 5015 and Mg b, for each galaxy The absorption line maps show that many galaxies contain some younger populations (<= 1 Gyr), distributed in small or large inner discs, or in circumnuclear star forming rings. In many cases these young stars are formed in circumnuclear mini-starbursts, which are dominating the light in the centres of some of the early-type spirals. These mini-starburst cause a considerable scatter in index-index diagrams such as Mg b- H beta and Mg b -Fe 5015, more than is measured for early-type galaxies. We find that the central regions of Sa galaxies display a wide range in ages, even within the galaxies. 50% of the sample show velocity dispersion drops in their centres. All of the galaxies of our sample lie on or below the Mg b- $\sigma$ relation for elliptical galaxies in the Coma cluster, and above the H beta absorption line - $\sigma$ relation for elliptical galaxies. If those relations are considered to be relations for the oldest local galaxies we see that our sample of spirals has a considerable scatter in age, with the largest scatter at the lowest $\sigma$. This is in disagreement with highly inclined samples, in which generally only old stellar populations are found in the central regions. All this can be understood if ... (see paper for rest of abstract)