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On the Relation Between Circular Velocity and Central Velocity Dispersion in High and Low Surface Brightness Galaxies1 A

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The Astrophysical Journal, 631:785–791, 2005 October 1 A # 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A. ON THE RELATION BETWEEN CIRCULAR VELOCITY AND CENTRAL VELOCITY DISPERSION IN HIGH AND LOW SURFACE BRIGHTNESS GALAXIES1 A. Pizzella,2 E. M. Corsini,2 E. Dalla Bonta`,2 M. Sarzi,3 L. Coccato,2 and F. Bertola2 Received 2005 January 5; accepted 2005 March 24 ABSTRACT In order to investigate the correlation between the circular velocity Vc and the central velocity dispersion of the spheroidal component c , we analyzed these quantities for a sample of 40 high surface brightness (HSB) disk galaxies, eight giant low surface brightness (LSB) spiral galaxies, and 24 elliptical galaxies characterized by flat À1 À1 rotation curves. Galaxies have been selected to have a velocity gradient 2kms kpc for R 0:35R25.Weused these data to better define the previous Vc-c correlation for spiral galaxies (which turned out to be HSB) and elliptical galaxies, especially at the lower end of the c values. We find that the Vc-c relation is described by a linear À1 law out to velocity dispersions as low as c 50 km s , while in previous works a power law was adopted for À1 galaxies with c > 80 km s . Elliptical galaxies with Vc based on dynamical models or directly derived from the H i rotation curves follow the same relation as the HSB galaxies in the Vc-c plane. On the other hand, the LSB galaxies follow a different relation, since most of them show either higher Vc or lower c with respect to the HSB galaxies. This argues against the relevance of baryon collapse to the radial density profile of the dark matter halos of LSB galaxies. Moreover, if the Vc-c relation is equivalent to one between the mass of the dark matter halo and that of the supermassive black hole, then these results suggest that the LSB galaxies host a supermassive black hole (SMBH) with a smaller mass compared to HSB galaxies with an equal dark matter halo. On the other hand, if the fundamental correlation of SMBH mass is with the halo circular velocity, then LSB galaxies should have larger black hole masses for a given bulge dispersion. Elliptical galaxies with Vc derived from H i data and LSB galaxies were not considered in previous studies. Subject headings: black hole physics — galaxies: elliptical and lenticular, cD — galaxies: fundamental parameters — galaxies: halos — galaxies: kinematics and dynamics — galaxies: spiral Online material: color figure 1. INTRODUCTION fective radius. As a consequence, the maximum circular veloc- A possible relation between the central velocity dispersion ity is correlated with the central velocity dispersion of the gal- axy (Gerhard et al. 2001). Whether the same is true for more of the spheroidal component ( ) and the galaxy circular veloc- c flattened and fainter elliptical galaxies is still to be investigated. ity measured in the flat region of the rotation curve (V )was c On the other hand, both the shape and amplitude of the rota- suggested by Whitmore et al. (1979) and Whitmore & Kirshner tion curve of a spiral galaxy depend on the galaxy luminosity (1981). By measuring H i line widths, they found that V / 1:7 c c and morphological type (e.g., Burstein & Rubin 1985; Persic for a sample of S0 and spiral galaxies. Recently, Ferrarese (2002) et al.1996). For this reason, for spiral galaxies the V - relation proceeded further, extending the V - relation to elliptical gal- c c c c is not expected a priori. axies. She interpreted the V - relation as suggestive of a c c It is interesting to investigate whether the V - relation also correlation between two different galactic components, since c c holds for less dense objects characterized by a less steep po- c and Vc probe the potential of the spheroidal component and of the dark matter (DM) halo, respectively. In particular, it re- tential well. This is the case for low surface brightness (LSB) galaxies, which are disk galaxies with a central face-on surface sults that for a given DM halo the central velocity dispersion of brightness 22:6 mag arcsecÀ2 (e.g., Schombert et al. 1992; the spheroidal component is independent of the morphological B Impey et al. 1996). Previous work concentrated on high surface type. The validity of this relation has been confirmed by Baes brightness (HSB) galaxies, and to infer the V for elliptical gal- et al. (2003), who enlarged the sample of spiral galaxies. c axies, they relied on stellar dynamical models. In this work we For elliptical galaxies, V is generally inferred by means c investigate the behavior of elliptical galaxies with H i–based V of dynamical modeling of the stellar kinematics. This is the c and of LSB galaxies in the V - relation. case for the giant round and almost nonrotating elliptical gal- c c This paper is organized as follows. An overview of the axies studied by Kronawitter et al. (2000). These galaxies form properties of the sample galaxies, as well as an analysis of the a unique dynamical family that scales with luminosity and ef- kinematic data available in the literature to derive their Vc and c, are presented in x 2. The results and discussion concerning 1 Based on observations made with European Southern Observatory tele- the Vc-c relation are given in x 3. scopes at the Paranal Observatory under programs 67.B-0283, 69.B-0573, and 70.B-0171. 2. SAMPLE SELECTION 2 Dipartimento di Astronomia, Universita` di Padova, vicolo dell’Osserva- torio 2, I-35122 Padova, Italy. In the past years we started a scientific program aimed at 3 Physics Department, University of Oxford, Keble Road, Oxford OX1 deriving the detailed kinematics of ionized gas and stars in HSB 3RH, UK. and LSB galaxies in order to study their mass distributions and 785 786 PIZZELLA ET AL. Fig. 1.—Deprojected rotation curves of the eight LSB galaxies of the final sample. structural properties. We measured the velocity curves and that were not characterized by an outer flat portion. Ferrarese velocity dispersion profiles along the major axis for both the (2002) and Baes et al. (2003) considered galaxies with the ro- ionized-gas and stellar components for a preliminary sample tation curve extending farther out than R25. This criterion is not of 50 HSB galaxies (10 S0–S0/a galaxies in Corsini et al. appropriate when the sample of galaxies spans a wide range in [2003]; seven Sa galaxies in Bertola et al. [1996] and Corsini photometric properties. For LSB galaxies, which have a lower et al. [1999]; 16 S0–Sc galaxies in Vega Beltra´n et al. [2001]; central surface brightness than HSB galaxies, R25 corresponds and 17 Sb–Scd galaxies in Pizzella et al. [2004b]) and 11 LSB to a relatively small radius, where the rotation curve may be still galaxies (A. Pizzella et al. 2005, in preparation; Pizzella et al. rising. For this reason we adopt a criterion that selects rota- 2004a). tion curves on the basis of their flatness rather then on their The HSB sample consists of disk galaxies with Hubble type extension. ranging from S0 to Scd, an inclination i 30, and a distance The flatness of each rotation curve has been checked by D < 80 Mpc. The LSB sample consists of disk galaxies with fitting it with a linear law, V(R) ¼ AR þ B for R 0:35R25. Hubble type ranging from Sa to Irr, an intermediate inclina- The radial range has been chosen in order to avoid the bulge- tion (30 P i < 70), and a distance D < 65 Mpc (except for ESO dominated region of the rotation curve (e.g., IC 724 and NGC 534-G20). Three LSB galaxies, namely, ESO 206-G14, ESO 2815). The rotation curves with jAj2kmsÀ1 kpcÀ1 within 488-G49, and LSBC F563-V02, have been selected from the 3 have been considered not to be flat. In this way 15 HSB gal- sample observed by de Blok & McGaugh (1997). The remain- axies and eight LSB galaxies resulted as having a flat rotation ing eight objects are LSB galaxies with bulge. They have been curve. Since the velocity curves of the LSB galaxies were not pre- selected in Lauberts & Valentijn (1989, hereafter ESO-LV) to sented in previous papers, we show their folded rotation curves have a LSB disk component following the criteria described by in Figure 1. We derived Vc by averaging the outermost values of Beijersbergen et al. (1999). Due to the bulge light contribution, the flat portion of the rotation curve. the total central face-on surface brightness of the galaxy could be We are therefore confident that we are giving a reliable es- À2 B 22:6 mag arcsec . However, all these objects do have a timate of the asymptotic value of the circular velocity that traces LSB disk. As far as their total luminosity is concerned, LSBC the mass of the DM halo (for a discussion, see Ferrarese 2002). F563-V02 and ESO 488-G49 are two dwarf LSB galaxies, but We derived c from the stellar kinematics by extrapolating the the other nine objects are representative of giant LSB galaxies velocity dispersion radial profile to r ¼ 000. This has been done (e.g., McGaugh et al. 2001). by fitting the eight innermost data points with an empirical func- For all the HSB and LSB galaxies, we obtained the ionized- tion (either an exponential, a Gaussian, or a constant). We did not gas rotation curve by folding the observed line-of-sight ve- apply any aperture correction to c, as discussed by Baes et al.
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  • Arxiv:1207.4189V1 [Astro-Ph.CO] 17 Jul 2012 N a Osdrtrefnaetlpyia Parame- Physical Fundamental Mass Three Alternatively, Ters: Consider Color

    Arxiv:1207.4189V1 [Astro-Ph.CO] 17 Jul 2012 N a Osdrtrefnaetlpyia Parame- Physical Fundamental Mass Three Alternatively, Ters: Consider Color

    The Astrophysical Journal Supplement Series, in press, 17 July 2012 A Preprint typeset using LTEX style emulateapj v. 5/2/11 ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED Aaron J. Romanowsky1, S. Michael Fall2 1University of California Observatories, Santa Cruz, CA 95064, USA 2Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA The Astrophysical Journal Supplement Series, in press, 17 July 2012 ABSTRACT Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j⋆ and mass M⋆ (thus extending the work by Fall 1983). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as ten effective radii, and find that data at two effective radii are generally sufficient to estimate total j⋆ reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j⋆ in their outer regions owing to angular momentum transport in major mergers. We then carry out a comprehensive analysis of extended kinematic data from the literature for a sample of 100 nearby bright galaxies of all types, placing them on a diagram of ∼ j⋆ versus M⋆. The ellipticals and spirals form two parallel j⋆–M⋆ tracks, with log-slopes of 0.6, which for the spirals is closely related to the Tully-Fisher relation, but for the ellipticals derives from∼ a remarkable conspiracy between masses, sizes, and rotation velocities.