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GHASP : AN Hα KINEMATICAL SURVEY
Olivia Garrido 1,2, Philippe Amram 1, Michel Marcelin 1, Chantal
Balkowski 2, Claude Carignan 3, Jean-Luc Gach 1
GHASP (Gassendi HAlpha survey of SPirals) is a survey led at the 1.93m telescope of the Observatoire of
Haute-Provence (France). Many researchers of different institutes are involved in GHASP : Laboratoire
d’Astrophysique de Marseille (1), Observatoire de Paris-Meudon (2) and Université de Montréal (3). GHASP
mapped the distribution of ionized gas for 220 nearby (v<10 000 km/s) isolated Spirals and Irregulars,
observing the Hα line using a scanning Fabry-Perot and a photon-counting system (Gach et al. 2002). The
kinematics of warm gas has been derived providing 2D velocity fields and rotation curves. By now, 96 galaxies
have been reduced (Garrido et al., 2002, 2003 and 2004).
GHASP provides an homogeneous sample of 2D velocity fields covering the plane : absolute
magnitude- morphological type (Fig.1).
Fig.1 : Distribution of the 220 GHASP galaxies in the plane
absolute magnitude- morphological type.
Two examples of galaxies observed by GHASP are shown in this poster : UGC 5253
(Sab) and UGC 6778 (Sc). Up to bottom, we present in Fig.2 : the Hα map, the velocity
field with isovelocity lines superimposed and the rotation curve. The software ADHOCw
(developped by J. Boulesteix) used for the reduction of the data as well as the Hα maps,
the velocity fields and the rotation curves of the 96 reduced galaxies are available on our
Web site : http://www-obs.cnrs-mrs.fr/interferometrie/GHASP/observaghasp.html.
A databate is being built and the data could be obtained simply sending an e-mail to
[email protected] (or [email protected]).
In order to study the fluctuation of the inner slope, the outer slope, the degree of
asymmetry of the rotation curves, the extension of the ionized disk and the Tully-Fisher
relation (Garrido et al., 2004), each rotation curve has been fitted with the profile
defined by Kravtsov et al. (1998) :
V ( r ) = Vt
Fig.2: Examples of 2 galaxies observed by GHASP.
Fig.4 : Extension of the ionized disk (Rlast) in units of R25
versus the morphological type.
r 
 r
 t
g
a
 

r 
1 +  rt  


g +b
a
Fig.3 : Central surface brightness
versus the inner slope of the rotation
curve.
We found a loose correlation between
the inner slope of the rotation curve
and the morphological type or the
absolute magnitude. In fact, the inner
velocity gradient is directly
correlated with the central
concentration of light.
We confirm the trend already mentioned by Marquez et
al. (2002) and Rubin et al. (1999) that the Rlast/R25 ratio
varies according to the morphological type. We observe
massive star formation all over the optical disk and up to
1.5R25 for Sbc to Sd galaxies. Early type galaxies have
minima sizes of the ionized disk; their low mean HI
surface density is not sufficient at the end of the disks for
the star formation to begin (Kennicutt, 1989). In the case
of Irregulars (which are rich in neutral gas), the high
dispersion of the velocities prevents the collapse of the
gas clouds at the end of the optical disk.
Fig.5 : Asymmetry of the rotation curves versus t, MB and the (B-V) color. The asymmetry has been calculated
using the formula of Dale et al. (2003) which considers the difference between both sides of the rotation curve
but also the dispersion of the velocity points.
Lopsidedness in galaxies is very common (50% of the HI profiles are asymmetric; Haynes et al., 1998;
warps in U-shape of the disks; asymmetry in light distribution). Conselice (1997) found that asymmetry
in the light distribution is strongly correlated with t and the color of the galaxy. Asymmetry in rotation
curves is also well correlated with t, MB and the color of the galaxy. Then, asymmetry in mass
distribution is directly linked with asymmetry in luminous matter distribution. Asymmetry in mass
distribution seems to be an intrinsic parameter and to have a secular origin (massive local star
formation) since the relations of Fig.5 disappear when considerating cluster galaxies which are disturbed
by environment (Rubin et al., 1999; Dale et al., 2001).
GHASP will provide an homogeneous reference sample at z=0 of 2D Hα velocity fields for 220 isolated Spirals and Irregulars. It will allow to study the
mass distribution all along the Hubble sequence, the environmental effects, the inner kinematics with help of simulation and the evolution of galaxies
when comparing with 2D kinematics of distant galaxies with nearby ones.