gaseous bidimensional velocity fields of spiral galaxies with vlt/vimos integral field unit

GASEOUS BIDIMENSIONAL VELOCITY FIELDS OF SPIRAL GALAXIES WITH VLT/VIMOS

INTEGRAL FIELD UNIT

Lodovico Coccato(Kapteyn Astronomical Institute, Groningen - NL)

People involved:F. Bertola, E.M. Corsini, A. Pizzella - Padova University, ItalyS. D’Odorico - ESO Garching, GermanyK. Fathi - Rochester Institute of Technology, USAD.C. Hunter - Lowell Observatory, USAS. McGaugh, R. Swaters - University of Maryland, USAV. Rubin - Dept. of Terrestrial Magnetism, CIW, USA

Overview of the talk:

We present the data in 2 parts, regarding 2 different projects:

1. The study and the characterization of Inner Polar Disks (IPDs) in early-type spirals galaxies (Coccato et al.

2006, A&A submitted).

2. The central mass density profile in Low Surface Brightness galaxies (LSBs) using 2D kinematics of star and gas. (Coccato et al 2007, in preparation)

The study of IPDs: The case of NGC 2855 and NGC 7049

Gaseous Inner Polar Disks in spiral galaxies

In a recent paper we pointed out that ~ 50% of bright unbarred galaxies shows a remarkable gaseous velocity gradient along the minor axis (Coccato et al. 2004)

Non circular motions for the gas are very common

General results obtained with the circular assumption may be completely wrong!!!

New additional evidences by SAURON observations in 2D velocity fields (Sarzi et al. 2006; Falcon Barroso et al. 2006; Ganda et al. 2006).

What can generate a central velocity gradient along the minor axis?

a) Outflows, triaxial potential, bars…

b) Inner Polar Disk (that’s what we are interested in)


IPDs: A polar gaseous and/or stellar structures rotating in an orthogonal plane with respect to the main galaxy disk (see Corsini et al. 2003 and Sil’chenko 2004 for references).Small, located in the centre of the galaxies (R ~ 0.3 - 1 kpc).

Literature: ~20 objects. Corsini et al. 2003, Sil’chenko & Afanazief 2004; Shalyapina et al. 2004; Sil’chenko & Moiseev 2005, Sil’chenko 2006…

Structure: Two orthogonal gaseous disk (geometrical decoupling) or strong warp in the innermost regions (warp with orbits ~ 90°)

Origin: External gas acquisition in a direction close to the minor axis ( geometrical decoupling); a triaxial bulge or a bar which is tumbling about its short axis can transfer the gas from the main disk onto highly inclined anomalous orbits ( strong inner warp) Understanding the geometry is a key to understand the origin.


Signature: long slit: Minor axis velocity gradient + major axis central plateau.


Signature: 2D integral field: S-shaped distortion of the 2D field.


Candidates: Large program to select IPD candidates by means of long slit spectroscopy (mainly S0/Sa, Sa galaxies: Corsini et al. 2002, 2003; Coccato et al. 2004,2005; Sarzi et al. 2000; Bertola et al. 1999 )

The “best” candidates are the galaxies with a central velocity gradient along the minor axis + a central plateau along the major axis.(if we do not have the central plateau the most likely scenario is the elliptical orbits in a triaxial potential: see de Zeeuw & Franx 1989)Those long-slit selected candidates are going to be the target for the 2D follow-up

We present here the 2D kinematics of two Sa galaxies NGC 2855 and NGC 7049, our most promising candidates.


Stellar (filled circles) and ionized-gas (open circles) kinematics measured along major (left panels) and minor (right panels) axis of the sample galaxies. Error bars smaller than symbols are not plotted. The gaseous component shows a central plateau along the major axis and a central velocity gradient along the minor axis. From Corsini et al. 2003.

NGC 2855 NGC 7049

VIMOS FOV 27”x27”

(DSS images 5’ x 5’)



VIMOS/IFU observations of NGC 2855 and NGC 7049:

Observations:2 OBs x target each OB with 2x19 min. exp. time (total: 76 min. per galaxy)

Reduction:ESOrex + MIDAS (cosmic rays removal)

Measures:Gaussian fit to the emission lines H & [NII]


Analysis of the velocity field

The field of view is large enough to map the inner decoupled component as well as (part of) the main disk (circular motions).

The first step is to constrain the main disk kinematics and geometry and then try to analyze the decoupled part.

The main disk kinematics and geometry is derived with a circular model.

The decoupled innermost region is studied using two different models:

1) Two orthogonally decoupled gaseous disks 2) A tilted ring model simulating a strong central warp.


Circular model – main gaseous disk properties

We masked the central regions with the S-shape and fit a circular model to the data, in order to constrain the main gaseous disk (circular velocity, inclination, position angle)

Assumptions:

1) The main disk is moving onto circular orbits in an infinitesimally thin disk with negligible velocity dispersion.

2) The circular velocity follows the empirical formula:


Results for the circular model

Main galaxy disc (see circular model)

Inner Polar Disk


The 2 components are allowed to have different velocity fields and different surface brightness profiles

Orthogonally-rotating disks

)/exp()( 10 FRRFFRF

IPDMAIN

IPDIPDMAINMAINOBS FF

FVFVV


Fit #1 (geometry/SB check): fit only the surface brightness profile. Parameters:1) F0, F1 and RF for the main disk and the IPD (free parameters).2) Inclination (constrained 89 < < 91) and (free parameters)

Fit #2 (velocity check): fit only the velocity fields. Parameters:1) Vmax and Rh for the velocity the main disk (from the circular model)2) Flux parameters of the 2 disks (from Fit #1)3) Orientation of the MD (from circular model) and the IPD (from Fit #1)4) Vmax and Rh for the velocity the IPD (free parameters)

Fit #3 (geometry/SB + velocity check): simultaneous fit of the surface brightness and the velocity field. Parameters:1) F0, F1 and RF for the main disk and the IPD (free parameters).2) Vmax and Rh for the velocity the main disk (from the circular model) and the IPD (free parameters)3) Inclination (constrained 89 < < 91) and (free parameters)4) Orientation of the MD (from circular model).


Dots: observed isophotal analysisSolid line isophotal analysis on Fit #1

Results for the two orthogonal disks (Fit #1)


ONLY FIT #1 FOR NGC 7049 IS GOOD!!!


Tilted rings - Warp model

orthogonal in the center

Inclination decreasing for outer radii


Tilted rings-Warp model:

1. Circular motions but onto tilted rings. General shape for the circular velocity is assumed to be:

2. The lines of nodes (intersection between the galaxy main plane and the rings) has a linear variation.

3. The inclination of the rings is ~90° in the centre, and ~0° in the outer regions.

With assumptions #2 and #3 we are able to reproduce the shape of ellipticity and position angle.

4. No assumption for the flux: we used the observed emission lines.


IT WORKS ONLY FOR NGC 2855 !!!

Results for the tilted ring - warp model

How is the warp generated in NGC 2855?

We can exclude that the IPD/warped disk in NGC 2855 is due to gas moving onto anomalous orbits in the triaxial bulge or bar that is tumbling around the minor axis because:

a) No bar structure is observed in optical (Corsini et al. 2002) nor in the IR (Peletier et al. 1999)

b) No evidence of gas in retrograde motion relative to the stars mandatory for the anomalous orbits equilibrium (van Albada et al 1982; Friedly & Benz 1993)


How is the warp generated in NGC 2855?Evidence of accretion for NGC 2855 (Malin & Hadley 1997): the accreting material is forming the warped structure.


Conclusions for the IPD analysis:

1) 2D spectroscopy of NGC 2855 and NGC 7049 with VLT/VIMOS. They both show an S-shaped distortion of the isovelocities.

2) We modeled the velocity field of the main galaxy disk with a thin disk in circular motions in order to characterize its properties (circular velocity, inclination and position angle)

3) We build two models to analyze the central kinematics: two orthogonal-disk and tilted ring models. Both galaxies are consistent with the IPD scenario: two orthogonal disks for NGC 7049 and single warped disk for NGC 2855.

4) In NGC 7049 the gas is already settled in the equilibrium planes of the triaxial bulge, the velocity field of the IPD is not characterized by circular motions (at least, the arctan function is not working).

5) Deep imaging of NGC 2855 suggests that the internal warp in NGC 2855 has an external origin.



Conclusions for the IPD analysis:6) Underrating of the true velocity gradient

Stellar and gaseous velocity fields of a LSB galaxy

Stellar and gaseous velocity fields of ESO323-G064

BackgroundLow surface brightness galaxies (LSBs) are the ideal laboratories to study the dark matter (DM) distribution in galaxies, since they are DM dominated.So far, the majority of kinematical studies were based on long slit spectroscopy of the ionized gas and the radio 21-cm under the assumption of circular motions.

Results collected so far show that a pseudo isothermal halo model better describes the mass density profile for the dark matter halo.

Light blue: pseudo isothermal haloRed: NFWGreen: CDMr-1.5 Moore et al 1999

(De Blok et al 2001)


2

2)(4

r

V

r

V

r

VrG

However, gaseous kinematics in LSB seems to be dominated by non circular motions (Tamburro, laurea thesis 2004, Pizzella et al 2003). Stellar motions are more reliable.


Minor (upper panels) and major (lower panels) kinematics of stars (left panels) and gas (right panels) for the LSB galaxy ESO 189-07

(From Pizzella et al. 2003)


ESO 323G-064We decided to observe the LSB galaxy ESO 323-G064 in order to derive the correct mass density profile using both stellar and gaseous kinematics.We used the HR-B grating (4120-6210 Angstrom, R~1700, 0”67x0”67 “/fibre)

V=14520 km/sec, D=194 Mpc (Ho=75 km/s/Mpc)

2 Observed fields (4x30 min for each field)

F.O.V.: 27” x 27”

VIMOS reconstructed image



IONIZED GAS KINEMATICSCentral regions are characterized by 3-peaked emission lines

H [OIII] 4959, 5007 ang

(In the picture only [OIII] is shown)


km/sec 14530 5050

V

km/sec 14720 9070

V

km/sec 15000 9070

V


Circular velocity curve extracted from the 2D velocity field


(FOV 14” x 14”)

Stellar velocity field


FOV 14” x 14”

Stellar velocity dispersion

~80 < < ~200 km/s


…Example of the stellar data quality

…Discussion, results, work still in progress

Complex gaseous velocity field (3 peaks in the emission lines)

The stellar velocity field shows a more regular rotation in the innermost regions with respect to the ionized gas component

The stellar radial velocity ranges from ~14650 to ~15000 km/s (correction for inclination not applied)

The stellar velocity dispersion ranges from ~200 km/s in the centre to ~ 80 km/s at the edges.

Modeling is still in progress to derive the central velocity gradient.We are going to explore, just to start, 2 cases: a) stars in a thin disk with the asymmetric drift correction b) spherical, isotropic distribution (Jeans models)


-- Summary --

1) VIMOS/IFU observations of NGC 2855 and NGC 7049, candidates for hosting an IPD. Both kinematics are consistent with a geometrical orthogonal decoupling (NGC 7049) or a strong inner warp (NGC 2855)

2) VIMOS/IFU observations of the LSB galaxy ESO323-G064: complex gaseous velocity field (3 nuclear components) and a regular stellar velocity and velocity dispersion fields. Models for the correct measurement of are still in progress

gaseous bidimensional velocity fields of spiral galaxies with vlt/vimos integral field unit

Documents

case of ngc

d field

d integral field

inthe study of ipds

minor axis coccato

central velocity gradient

d velocity fields sarzi

sa galaxies