In order to investigate the correlation between the circular velocity Vc and
the central velocity dispersion of the spheroidal component sigma_c, we
analyzed these quantities for a sample of 40 high surface brightness disc
galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies
(hereafter LSB), and 24 elliptical galaxies characterized by flat rotation
curves. We find that the Vc-sigma_c relation is descri ed by a linear law out
to velocity dispersions as low as sigma_c~50km/s, while in previous works a
power law was adopted for galaxies with sigma_c>80k/ms.
  Elliptical galaxies with Vc based on dynamical models or directly derived
from the HI rotation curves follow the same relation as the HSB galaxies in the
Vc-sigma_c plane. On the contrary, the LSB galaxies follow a different
relation, since most of them show either higher Vc (or lower sigma_c) with
respect to the HSB galaxies. This argues against the relevance of baryon
collapse in the radial density profile of the dark matter haloes of LSB
galaxies. (abridged)Comment: 18 pages, 4 figures, ApJ in pres

A. Pizzella

Beijersbergen M.

Carollo C. M.

Corsini E. M.

de Blok W. J. G.

E. Dalla Bonta

E. M. Corsini

F. Bertola

Guthrie B. N. G.

Jorgensen I.

L. Coccato

M. Sarzi

Persic M.

Sandage A.

English

arXiv

Crossref

On the Relation between Circular Velocity and Central Velocity Dispersion in High and Low Surface Brightness Galaxies

In order to investigate the correlation between the circular velocity V_c and the central velocity dispersion of the spheroidal component σ_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 rotation curves. Galaxies have been selected to have a velocity gradient =0.35 R_25. We used these data to better define the previous V_c-σ_c correlation for spiral galaxies (which turned out to be HSB) and elliptical galaxies, especially at the lower end of the σ_c values. We find that the V_c-σ_c relation is described by a linear law out to velocity dispersions as low as σ_c~50 km/s, while in previous works a power law was adopted for galaxies with σ_c>80 km/s. Elliptical galaxies with V_c based on dynamical models or directly derived from the H I rotation curves follow the same relation as the HSB galaxies in the V_c-σ_c plane. On the other hand, the LSB galaxies follow a different relation, since most of them show either higher V_c or lower σ_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 V_c-σ_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 V_c derived from H I data and LSB galaxies were not considered in previous studies

PIZZELLA, ALESSANDRO

CORSINI, ENRICO MARIA

DALLA BONTA', ELENA

COCCATO, LODOVICO

BERTOLA, FRANCESCO

SARZI M.

Archivio istituzionale della ricerca - Università di Padova

On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies

We analyzed a sample of high and low surface brightness (HSB and LSB) disc galaxies and elliptical galaxies to investigate the correlation between the circular velocity (V_c) and the central velocity dispersion (sigma_c). We better defined the previous V_c-sigma_c correlation for HSB and elliptical galaxies, especially at the lower end of the sigma_c values

COCCATO L.

CIRCULAR VELOCITY AND CENTRALVELOCITY DISPERSION INLOW SURFACE BRIGHTNESS GALAXIESE.M. Corsini1∗, A. Pizzella1, E. Dalla Bontà1, F. Bertola1, L. Cocato2 andM. Sarzi31Dipartimento di Astronomia, Università di Padova, Italy2Kapteyn Astronomical Institute, University of Groningen, The Netherlands3Physics Department, University of Oxford, UK* corsini@pd.astro.itAbstract We analyzed a sample of high and low surface brightness (HSB and LSB) discgalaxies and elliptical galaxies to investigate the correlation between the circularvelocity (Vc) and the central velocity dispersion (σc). We better defined theprevious Vc– σc correlation for HSB and elliptical galaxies, especially at thelower end of the σc values.Elliptical galaxies with Vc based on dynamical models or directly derivedfrom the Hi rotation curves follow the same relation as the HSB galaxies in theVc– σc plane. On the contrary, the LSB galaxies follow a different relation, sincemost of them show either higher Vc (or lower σc) with respect to the HSB galax-ies. This argues against the relevance of baryon collapse in the radial densityprofile of the dark matter haloes of LSB galaxies. Moreover, if the Vc– σc re-lation is equivalent to one between the mass of the dark matter halo and that ofthe supermassive black hole, these results suggest that the LSB galaxies host asupermassive black hole with a smaller mass compared to HSB galaxies of equaldark matter halo. On the other hand, if the fundamental correlation of SMBHmass is with the halo Vc, then LSBs should have larger black hole masses forgiven bulge σc.Keywords: galaxies: elliptical and lenticular, cD – galaxies: fundamental parameters –galaxies: kinematics and dynamics – galaxies: spirals1. IntroductionA possible relation between the central velocity dispersion of the spheroidalcomponent (σc) and the galaxy circular velocity (Vc) measured in the flat re-gion of the rotation curve (RC) was suggested by Whitmore et al. (1979). Bymeasuring stellar velocity dispersions and Hi line widths for a sample of 1977C© 2007 Springer.R. S. de Jong, Island Universes, 77–82.78 ISLAND UNIVERSESspiral galaxies they found a a significant decrease in Vc/σc with increasingbulge-to-disk ratio. Since σc and Vc probe the potential of the spheroid anddark matter (DM) halo, a mean value Vc/σc  1.7 implies these componentsare dynamically separate with the bulge substantially cooler than halo.Gerhard et al. (2001) derived the Vc–σc relation for the sample of giantelliptical galaxies studied by Kronawitter et al. (2000). This was explained asan indication of near dynamical homology of these objects which were selectedto be nearly round and almost non-rotating elliptical galaxies. These galaxiesform a unique dynamical family which scales with luminosity and effectiveradius. As a consequence the maximum Vc of the galaxy is correlated to its σc.Whether the same is true for more flattened and fainter ellipticals is still to beinvestigated. On the contrary, both shape and amplitude of the RC of a spiralgalaxy depend on the galaxy luminosity and morphological type (e.g., Burstein& Rubin 1985). As a consequence for spiral galaxies the Vc–σc relation is notexpected a priori.Nevertheless, Ferrarese (2002) and Baes (2003) found that elliptical andspiral galaxies define a common Vc–σc relation. In particular, they find thatfor a given σc the value of Vc is independent of the morphological type. Butσc and Vc are related to the mass of the supermassive black hole (hereafterSMBH, see Ferrarese & Ford 2005 for a review) and DM halo (e.g., Seljak2002), respectively. Therefore Ferrarese (2002) argued that the Vc–σc relationis suggestive of a correlation between the mass of SMBH and DM halo.Previous works concentrated on high surface brightness (HSB) galaxies. Itis interesting to investigate whether the Vc–σc relation holds also for less denseobjects characterized by a less steep potential well. This is the case of lowsurface brightness (LSB) galaxies, which are disc galaxies with a central face-on surface brightness µB ≥ 22.6 mag arcsec−2 (e.g., Impey et al. 1996). InPizzella et al. (2005) we studied the behavior of LSB galaxies in the Vc–σcrelation. Here we present our results.2. Sample SelectionIn the past years we started a scientific program aimed at deriving the de-tailed kinematics of ionized gas and stars in HSB and LSB galaxies in or-der to study their mass distribution and structural properties (e.g., Pignatelli etal. 2001).We measured the velocity curves and velocity dispersion profiles along themajor axis for both the ionized-gas and stellar components for a preliminarysample of 50 HSB galaxies [10 S0–S0/a’s in Corsini et al. (2003); 7 Sa’s inBertola et al. (1996) and Corsini et al. (1999); 16 S0–Sc’s in Vega Beltranet al. (2001); 17 Sb–Scd’s in Pizzella et al. (2004a)] and 11 LSB galaxies(Pizzella et al. 2004b). The HSB sample consists of disc galaxies with HubbleThe Vc–σc Relation for LSB Galaxies 79type ranging from S0 to Scd, an inclination i ≥ 30◦ and a distance D <80 Mpc. The LSB sample consists of disc galaxies with Hubble type rangingfrom Sa to Irr, an intermediate inclination (30◦ ≤ i ≤ 70◦), and a distanceD < 65 Mpc. In order to complete our sample of disc galaxies we includedthe 38 Sa-Scd galaxies previously studied by Ferrarese (2002) and the 12 Sb-Scgalaxies by Baes et al. (2003).Finally, we considered a sample of 24 elliptical galaxies with a flat RC andfor which both Vc and σc are available from the literature. They include 19 ob-jects studied by Kronawitter et al. (2000) who derived Vc by dynamical mod-eling and 5 objects studied by Bertola et al. (1993) for which Vc is directlyderived from the flat portion of their Hi RCs. The addition of these galaxieswill allow to test against model-dependent biases in the Vc–σc relation.3. Measuring Vc and σcFor all the disc galaxies we obtained the ionized-gas RC. We rejected galax-ies with asymmetric RCs or RCs which were not characterized by an outer flatportion. The flatness of each RC has been checked by fitting it with a linear lawV (R) = AR+B for R ≥ 0.35 R25. The radial range has been chosen in or-der to avoid the bulge-dominated region. The RCs with |A| ≥ 2 km s−1 kpc−1within 3σ have been considered not to be flat. We derived Vc by averaging theoutermost values of the flat portion of the RC. We derived σc from the stellarkinematics by extrapolating the velocity dispersion radial profile to the centre.This has been done by fitting the innermost data points with an empirical func-tion (either an exponential, or a Gaussian or a constant). We did not apply anyaperture correction to σc as discussed by Pizzella et al. (2004a).For the elliptical galaxies we obtained Vc either from the dynamical modelsby Gerhard et al. (2001) or from the flat portion of the Hi RC. For these galaxieswe relaxed the flatness criterion in favor of their large radial extension whichis about 10 times larger than that of optical RCs. Aperture measurements ofthe stellar velocity dispersion corrected to re/8 were adopted to estimate σc.4. The Vc– σc Relation for HSB and Elliptical GalaxiesIn summary, we have 40 disc galaxies [15 from our preliminary sample, 16from Ferrarese (2002), and 9 from Baes et al. (2003) with flat RCs extendingto ∼ 0.8 R25] and 24 elliptical galaxies [19 from Kronawitter et al. (2000)with flat RCs extending to about ∼ 0.5 R25, 5 from Bertola et al. (1993) withflat Hi RCs extending to ∼ 3 R25].A power law has been usually adopted to describe the correlation betweenVc and σc for galaxies with σc> 80 km s−1. We findlog Vc = (0.74 ± 0.07) log σc + (0.80 ± 0.15) (1)80 ISLAND UNIVERSESFigure 1. The correlation between Vc and σc. The data points corresponding to HSB galaxies(filled circles), LSB galaxies (squares), and elliptical galaxies with Vc obtained from Hi data(diamonds) or dynamical models (crosses) are shown. The dash-dotted and continuous linerepresent the power-law (Eq. 1) and linear fit (Eq. 2) to HSB and elliptical galaxies. The dottedline represents the linear-law fit (Eq. 3) to LSB galaxies. For a comparison, the dashed linecorresponds to the power-law fit to spiral galaxies with σc > 80 km s−1 by Baes et al. (2003).with Vc and σc expressed in km s−1. The resulting power law is plotted inFig. 1 (dash-dotted line). However, according to a χ2 analysis the data arealso consistent with a linear law out to velocity dispersions as low as σc ≈ 50km s−1Vc = (1.32 ± 0.09)σc + (46 ± 14). (2)The resulting straight line is plotted in Fig. 1 (continuous line).The data points corresponding to the 5 elliptical galaxies with Vc based onHi data follow the same relation as the remaining disc and elliptical galaxies.They are mostly located on the upper end of the Vc–σc relation derived for discgalaxies, in agreement with the findings of Bertola et al. (1993). They studiedthese elliptical galaxies and showed that their DM content and distribution aresimilar to those of spiral galaxies.The Vc–σc Relation for LSB Galaxies 815. The Vc– σc Relation for LSB GalaxiesThe LSB and HSB galaxies do not follow the same Vc–σc relation. In fact,most of the LSB galaxies are characterized by a higher Vc for a given σc (or alower σc for a given Vc) with respect to HSB galaxies. By applying to the LSBdata points the same regression analysis which has been adopted for the HSBand elliptical galaxies of the final sample, we findVc = (1.35 ± 0.19)σc + (81 ± 23) (3)with Vc and σc expressed in km s−1. The straight line corresponding to this fit,which is different from the one obtained for HSB and elliptical galaxies andhappens to be parallel to it, is plotted in Fig. 1 (dotted line). To address thesignificance of this result, which is based only on 8 data points, we comparedthe distribution of the normalized scatter of the LSB galaxies to that of the HSBand elliptical galaxies. They are different at a high confidence level (> 99%)by a Kolmogorov-Smirnov test. The fact that these objects fall in a differentregion of the Vc–σc plane confirms that LSB and HSB galaxies constitute twodifferent classes of galaxies.6. ConclusionsBoth demographics of SMBHs and study of DM distribution in galacticnuclei benefit from the Vc–σc relation. The recent finding that the mass ofSMBHs correlates with different properties of the host spheroid supports theidea that formation and accretion of SMBHs are closely linked to the formationand evolution of their host galaxy. A task to be pursued is to obtain a firmdescription of all these relationships spanning a wide range of SMBH massesand address if they hold for all Hubble types. In fact, the current demographyof SMBHs suffers of important biases, related to the limited sampling overthe different basic properties of their host galaxies. The finding that the Vc–σcrelation holds for small values of σc points to the idea that SMBHs with massesM• < 106 M may also exist and follow the M•-σ relation.Moreover, it has been suggested that the Vc–σc relation is equivalent toone between the masses of SMBH and DM halo (Ferrarese 2002; Baes 2003)because σc and Vc are related to the masses of the central SMBH and DMhalo, respectively. Yet, this claim is to be considered with caution, as thedemography of SMBHs is still limited, in particular as far as spiral galaxiesare concerned. Furthermore, the calculation of the virial mass of the DM halofrom the measured Vc depends on the assumptions made for the DM densityprofile and the resulting rotation curve (e.g., see the prescriptions by Seljacket al. 2002). A better estimate of the virial velocity of the DM halo Vvir canbe obtained by constraining the baryonic-to-dark matter fraction with detaileddynamical modeling of the sample galaxies. The resulting Vvir−σc relation82 ISLAND UNIVERSESis expected to have a smaller scatter than the Vc–σc relation. If the M•-σrelation is to hold, the deviation of LSB galaxies with bulge from the Vc–σc ofHSB and elliptical galaxies suggests that for a given DM halo mass the LSBgalaxies would host a SMBH with a smaller mass compared to HSB galaxies.On the other hand, if the fundamental correlation of SMBH mass is with thehalo Vc, then LSBs should have larger black-hole masses for given bulge σc.This should be accounted for in the theoretical and numerical investigations ofthe processes leading to the formation of LSB galaxies.The collapse of baryonic matter can induce a further concentration in theDM distribution, and a deepening of the overall gravitational well in the centralregions. If this is the case, the finding that at a given DM mass (as traced by Vc)the central σc of LSB galaxies is smaller than in their HSB counterparts, wouldargue against the relevance of baryon collapse in the radial density profile ofDM in LSB galaxies.ReferencesBaes, M., Buyle, P., Hau, G. K. T., & Dejonghe, H. 2003, MNRAS, 341, L44Bertola, F., Cinzano, P., Corsini, E. M., et al. 1996, ApJ, 458, L67Bertola, F., Pizzella, A., Persic, M., & Salucci, P. 1993, ApJ, 416, L45Burstein, D., & Rubin, V. C. 1985, ApJ, 297, 423Corsini, E. M., Pizzella, A., Sarzi, M., et al. 1999, A&A, 342, 671Corsini, E. M., Pizzella, A., Coccato, L., & Bertola, F. 2003, A&A, 408, 873Ferrarese, L. 2002, ApJ, 578, 90Ferrarese, L., & Ford, H. 2005, Space Science Rev., 116, 523Gerhard, O., Kronawitter, A., Saglia, R. P., & Bender, R. 2001, AJ, 121, 1936Kronawitter, A., Saglia, R. P., Gerhard, O., & Bender, R. 2000, A&AS, 144, 53Impey, C. D., Sprayberry, D., Irwin, M. J., & Bothun, G. D. 1996, ApJS, 105, 209Pignatelli, E., Corsini, E. M, Vega Beltran, J. C., et al. 2001, MNRAS, 323, 188Pizzella, A., Corsini, E. M., Vega Beltran, J. C., & Bertola, F. 2004a, A&A, 424, 447Pizzella, A., Corsini, E. M., Bertola, F., et al. 2004b, IAU Symp., 222, 337Pizzella, A., Corsini, E. M., Dalla Bonta‘, et al. 2005, ApJ, 631, 785Seljak, U. 2002, MNRAS, 334, 797Vega Beltran, J. C., Pizzella, A., Corsini, E. M., et al. 2001, A&A, 374, 394Whitmore, B. C., Schechter, P. L., & Kirshner, R. P. 1979, ApJ, 234, 68

Circular velocity and central velocity dispersion in low surface brightness galaxies

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On the relation between circular velocity and central velocity
  dispersion in high and low surface brightness galaxies

On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies

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Archivio istituzionale della ricerca - Università di Padova

Archivio istituzionale della ricerca - Università di Padova