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Register a new userThe stellar mass distribution in early-type disk galaxies: surface photometry and bulge-disk decompositions
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We present deep B- and R-band surface photometry for a sample of 21 galaxies with morphological types between S0 and Sab. We present radial profiles of surface brightness, colour, ellipticity, position angle and deviations of axisymmetry for all galaxies, as well as isophotal and effective radii and total magnitudes. We have decomposed the images into contributions from a spheroidal bulge and a flat disk, using an interactive, 2D decomposition technique. We study in detail the relations between various bulge and disk parameters. In particular, we find that the bulges of our galaxies have surface brightness profiles ranging from exponential to De Vaucouleurs, with the average value of the Sersic shape parameter n being 2.5. In agreement with previous studies, we find that the shape of the bulge intensity distribution depends on luminosity, with the more luminous bulges having more centrally peaked light profiles. By comparing the ellipticity of the isophotes in the bulges to those in the outer, disk dominated regions, we are able to derive the intrinsic axis ratio q_b of the bulges. The average axis ratio is 0.55, with an rms spread of 0.12. None of the bulges in our sample is spherical, whereas in some cases, the bulges can be as flat as q_b = 0.3 - 0.4. The bulge flattening seems to be weakly coupled to luminosity, more luminous bulges being on average slightly more flattened than their lower-luminosity counterparts. Our finding that most bulges are significantly flattened and have an intensity profile shallower than R^{1/4} suggests that `pseudobulges, formed from disk material by secular processes, do not only occur in late-type spiral galaxies, but are a common feature in early-type disk galaxies as well. (abridged)
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We are studying the mass distribution in a sample of 50 early type spiral galaxies, with morphological type betweens S0 and Sab and absolute magnitudes M_B between -18 and -22; they form the massive and high-surface brightness extreme of the disk galaxy population. Our study is designed to investigate the relation between dark and luminous matter in these systems, of which very little yet is known. From a combination of WSRT HI observations and long-slit optical spectra, we have obtained high-quality rotation curves. The rotation velocities always rise very fast in the center; in the outer regions, they are often declining, with the outermost measured velocity 10-25% lower than the maximum. We decompose the rotation curves into contributions from the luminous (stellar and gaseous) and dark matter. The stellar disks and bulges always dominate the rotation curves within the inner few disk scale lengths, and are responsible for the decline in the outer parts. As an example, we present here the decompositions for UGC 9133. We are able to put tight upper and lower limits on the stellar mass-to-light ratios.
We present a set of bulge-disk decompositions for a sample of 71,825 SDSS main-sample galaxies in the redshift range 0.003<z<0.05. We have fit each galaxy with either a de Vaucouleurs (classical) or an exponential (pseudo-) bulge and an exponential disk. Two dimensional Sersic fits are performed when the 2-component fits are not statistically significant or when the fits are poor, even in the presence of high signal-to-noise. We study the robustness of our 2-component fits by studying a bright subsample of galaxies and we study the systematics of these fits with decreasing resolution and S/N. Only 30% of our sample have been fit with two-component fits in which both components are non-zero. The g-r and g-i colours of each component for the two-component models are determined using linear templates derived from the r-band model. We attempt a physical classification of types of fits into disk galaxies, pseudo-bulges, classical bulges, and ellipticals. Our classification of galaxies agrees well with previous large B+D decomposed samples. Using our galaxy classifications, we find that Petrosian concentration is a good indicator of B/T, while overall Sersic index is not. Additionally, we find that the majority of green valley galaxies are bulge+disk galaxies. Furthermore, in the transition from green to red B+D galaxies, the total galaxy colour is most strongly correlated with the disk colour.
We present rotation curves for 19, mostly luminous, early-type disk galaxies. Rotation velocities are measured from a combination of HI velocity fields and long-slit optical emission line spectra along the major axis. We find that the rotation curves generally rise rapidly in the central regions and often reach rotation velocities of 200 - 300 km/s within a few hundred parsecs of the centre. The detailed shape of the central rotation curves shows a clear dependence on the concentration of the stellar light distribution and the bulge-to-disk luminosity ratio: galaxies with highly concentrated stellar light distributions reach the maximum in their rotation curves at relatively smaller radii than galaxies with small bulges and a relatively diffuse light distribution. We interpret this as a strong indication that the dynamics in the central regions are dominated by the stellar mass. At intermediate radii, many rotation curves decline. The strength of the decline is correlated with the total luminosity of the galaxies, more luminous galaxies having on average more strongly declining rotation curves. At large radii, however, all declining rotation curves flatten out, indicating that substantial amounts of dark matter must be present in these galaxies too. A comparison of our rotation curves with the Universal Rotation Curve from Persic et al. (1996) reveals large discrepancies between the observed and predicted rotation curves; we argue that rotation curves form a multi-parameter family which is too complex to describe with a simple formula depending on total luminosity only. (abridged)
Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special AstrophysicalObservatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are overheated; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.
Understanding how bulges grow in galaxies is critical step towards unveiling the link between galaxy morphology and star-formation. To do so, it is necessary to decompose large sample of galaxies at different epochs into their main components (bulges and disks). This is particularly challenging, especially at high redshifts, where galaxies are poorly resolved. This work presents a catalog of bulge-disk decompositions of the surface brightness profiles of ~17.600 H-band selected galaxies in the CANDELS fields (F160W<23, 0<z<2) in 4 to 7 filters covering a spectral range of 430-1600nm. This is the largest available catalog of this kind up to z = 2. By using a novel approach based on deep-learning to select the best model to fit, we manage to control systematics arising from wrong model selection and obtain less contaminated samples than previous works. We show that the derived structural properties are within $sim10-20%$ of random uncertainties. We then fit stellar population models to the decomposed SEDs (Spectral Energy Distribution) of bulges and disks and derive stellar masses (and stellar mass bulge-to-total ratios) as well as rest-frame colors (U,V,J) for bulges and disks separately. All data products are publicly released with this paper and through the web page https://lerma.obspm.fr/huertas/form_CANDELS and will be used for scientific analysis in forthcoming works.
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