stellar populations in nuclear disks and spiral...

BULGES

NGC 7457

ESO 498-G5 NGC 4710

ESO 1129 NGC 4565

NGC 4594

FORMATION AND EVOLUTION OF BULGES

Classical bulge

Pseudobulge

Boxy/peanuts bulge

Presents in early type galaxies: lenticular, Sa

Very similar to elliptical : Mg2 - ; Dn - ; FP; SSP, R(1/4)

Some differences: fotometry shows young stellar populations

Formation trough dissipative collapse or merger events (theoretical)

Presents in late type galaxies: Sb and later type

Luminosity profile is exponential

They are flat component, with a disk kinematic

Star formation

Formed trough secular evolution slow rearrangement of disk material indicate no major merger (theoretical)

boxy/peanut bulges are parts of bars seen edge-on, have their origin in vertical instabilities of the disc and are somewhat shorter in extent than bars.

Their stellar population is similar to that of the inner part of the disc from which they formed.


Boxy/Peanut Bulges

Disk-like Bulges

Classical Bulges

Eggen et al. 1962

Sandage 1990

Gilmore & Wyse 1998

Kauffmann 1996

Baugh et al. 1996

Cole et al. 2000

Raha et al. 1991

Debattista et al. 2004

Martínez-Valpuesta et al. 2006

Aguerri et al. 2001

Fu et al. 2003

Eliche-Moral et al. 2006 Athanassoula 1992

Heller & Shlosman 1994

Shen & Sellwood 2004

Dissipative collapse

Presence of metallicity and α/Fe gradient (Kobayashi 2004).

Presence of metallicity gradient with flat profile of α/Fe (Pipino et al. 2008).

Merging events Secular evolution

IN THE CURRENT PARADIGM…

Absent (or very shallow) gradients in bulges (Bekki & Shioya 1999)

metallicity gradient rarely enhanced by secondary events of star formation (Hopkins et al. 2009).

Classical Bulges Disk-like Bulges

Different formation mechanism leave differences in the stellar populations and in their radial profiles

Gradients eventualy present could either be amplified (change of scalelength) or erased (disc heating) (Moorthy & Holtzman 2006)

Which is the relative importance of different mecchanism (is one dominant?)

Model predictions…

More constraints from comparison of stellar populations of disk and bulge


STELLAR POPULATION RELATED WITH THE ENVIRONMENT WHERE THE GALAXY FORM AND EVOLVE

CLUSTER

FIELD

Potential wheel formation stop the merging in cluster (Z >2)

Merging continue (Z < 1)

FIELD GALAXIES YOUNGER THAN CLUSTER COUNTERPART

OBSERVATION (elliptical and early type):

EXTENDED DATA FIELD YOUNGER AND HIGHER METALLICITY

CENTRAL VALUES NO DIFFERENCES BETWEEN CLUSTER AND FIELD GROUP

De la rosa et al. 2001 , Collobert et al 2006

Bernardi et al. 1998

Bought et al 1996

ENVIRONMENT

Central values and gradients

Environment Late type

GALAXIES SAMPLE SELECTION

14 BRIGHT, NEARBY, CLUSTER, GALAXIES

OBSERVATION AND DATA REDUCTION

STANDARD REDUCTION FOR LOW RESOLUTION DATA AQUIRED WITH [email protected]

KINEMATIC AND LINESTRENGTH ANALYSIS

1) ROTATION GALAXY VELOCITY AND ROTATION VELOCITY DISPERSION MEASURED

2) LINE STRENGTH OF LICK INDICES MEASUERED USING WORTHEY ET AL. 1994 DEFINITION

PHOTOMETRIC ANALYSIS

2D PHOTOMETRIC DECOMPOSITION TO DISENTAGNGLE BULGE FROM DISK

RESULTS……

…STEP BY STEP……

mailto:[email protected]

Consistency of results

Comparison with the lick system..

Comparison with litterature

MAJOR AXIS KINEMATICS AND LINE-STRENGTH

Rbd Rbd Rbd

Dis

c d

om

inate

d r

egio

n

Nucle

ar

regio

n

Bulg

e d

om

inate

d r

egio

n

ANALISYS OF THE STELLAR POPULATIONS

…RESULTS……

AGE METALLICITY AND /ENHANCEMENT

AGE METALLICITY and /ENHANCEMENT

CENTRAL VALUES

RADIAL PROFILES

PSEUDOBULGES

NGC 1292

CONCLUSIONS

LINE STRENGTH PROFILES

LINE STRENGTH CENTRAL VALUES

1) Most of the sample galaxies show no gradient in age (merging events ) but a negative gradient of metallicity. (dissipative collapse)

2) no gradient was measured in the [α/Fe] radial profiles for all the galaxies (No inside-out scenario expected from merging)

1) The value of /<Fe> is for most of the galaxies between solar and 0.3 ( This imply time-scale that can be very short for star formation)

2) More massive bulges are older, more metal rich and characterized by a fast star formation.

Star formation fast and homogeneus in the bulge

CENTRAL VALUES: H, Mg2, <Fe>-

IN LATER TYPE ?

STRUCTURAL PROPERTIES

CORRELATE

CHEMICAL PROPERTIES

Mg2, H, Fe

IN ELLIPTICAL GALAXIES

We found good correlation for <Fe>

Mg2, H still correlate

Hint they are steeper…

AGE AND METALLICITY CENTRAL VALUES

Model grids from Thomas et al. 2003

3 Gyr 12 Gyr


Hint that early type are older and metal richer than later type

Model grids from Thomas et al. 2003 T ≤ 0

T > 0

Very young

Young

Old

3 Gyr 12 Gyr


No relation found with morphological type

No relation found with the membership

Model grids from Thomas et al. 2003

Fornax

Pegasus

NGC 7582

3 Gyr 12 Gyr

Most of objects show solar value of /Fe while few have super solar /Fe


No relation found with morphological type

No relation found with the membership

3 clear different classes of ages

Relation age-metallicity

Very young

Young

Old

Important correlation with the central velocity rotation dispersion

More massive bulges are older, more metal rich

AGE AND METALLICITY RADIAL PROFILES

Metallicity is decreasing with the radius

Age shows no gradient

Grad[Z/H] = [Z/H] (center)- [Z/H] (1Rbd) (Mehlert et al. 2003)

Grad(Age) = Age (center)-Age (1Rbd) (Mehlert et al. 2003)

Collapse model produce metallicity gradient

Early-type Mehlert et al. 2003

Bulges Jabloka et al. 2007

AGE AND METALLICITY RADIAL PROFILES

No gradient found with the radius

Solar to super-solar value (result from central value)

Grad( /<Fe>) = /<Fe> (center)-/<Fe> (Rbd) (Mehlert et al. 2003)

Merger model do not produce gradient and produce solar /<Fe>

Collapse model produce /<Fe> gradient

THE GALAXIES SAMPLE

14 CLUSTER GALAXIES ( Ferguson 1989; Garcia 1983)

BRIGHT (BT < 15.5 Mag)

NEARBY GALAXIES (cz<4500 km s-1)

MORPHOLOGICAL TYPE: SPIRAL GALAXIES

Fornax, Eridanus, Pegasus, N7582

SPECTROSCOPIC OBSERVATIONS

2 RUNS AT [email protected] TELESCOPE

WAVELENGTH RANGE = 4700-6700 Å

DISPERSION = 1.98 Å/PIXEL

INSTRUMENTAL FWHM 6 Å

SPATIAL RESOLUTION = 0.314 ARCSEC

Calibration and Observation

BASIC CALIBRATION (bias, flat, HeAr calibration lamp)

SPECTRA TAKEN ALONG THE MAJOR AXIS

TYPICAL EXPOSURE TIME 2x3600 s S/N>35-40

2-5 LICK/VELOCITY STANDARD STARS (G, K spectral type)


KINEMATICS AND LINESTRENGTH

KINEMATICAL MEASUREMENTS

LINE STRENGTH MEASUREMENTS

Worthey et al.1994

dF

FEW

C

I

2

1

1

Atomic indices

dF

FEW

C

I

2

1

11

log5.221

Molecular indices

We measured the profiles along the major axis of the values of the rotation velocity (v), rotation velocity dispersion ()

We measured the values of the indices defined in the LICK/IDS system for all the those present in our range

They are => H, Fe5015, Mg1, Mg2, Mgb, Fe5270,Fe, 5335, NaD

LICK INDICES OVERVIEW Lick indices related with age metallicity and /Fe

Possible way to break the degeneracy…

(Whortey et al. 1994, Thomas et al.2003)

533528.0527072.0( FeFeMgMgFe b

Balmer lines (H, H …)

Stellar population age

The iron and magnesium lines

Metallicity

Mg/<Fe> or /<Fe>

Timescale of the star formation

PSEUDOBULGES - THE CASE OF NGC 1292

CLASSICAL BULGES PSEUDO-BULGES

Flattened disk like structures, may have secondary bars, rings, and/or spiral structure

Dynamically cold – rotation dominated

Formed from slow rearrangement of disk material – indicate no major merger

Usually in types Sbc and later

In globally blue galaxies

resemble little ellipticals whic happen to have a disc

dynamically hot -dispersion dominated

formed via violent relaxation during major merger

in types S0-Sbc

in globally red galaxies

Kormendy and Kennicut 2004 translate these general concepts in a list

cookbook rules

(The more apply, the safer the classification becomes)

Secu

lar

evo

luti

on

Merg

ing

/d

issi

pati

ve c

oll

ap

se


APPLICATION OF KORMENDY RULES TO OUR SAMPLE

S´ersic index (n < 2)

Most of the sample bulges have it (9/14) Ellipticity compared with Vmax/σ0

The apparent flattening of the bulge is similar to that of the disc

NGC 1292, NGC 1351

NGC 1292 satisfy all the conditions

pseudobulge

Outsider in the FJ relation

Forbes & Ponman (1999)

PSEUDOBUGES


STELLAR POPULATION

YOUNG AGE (T=3 Gyr)

LOW METAL CONTENTS ([Z/H] =-0.7)

OVERABUNDANCE [/Fe]=-0.12

CENTRAL REGIONS ARE: R

adiu

s

DATING THE FORMATION OF THE COUNTER-ROTATING STELLAR DISC IN THE SPIRAL GALAXY NGC 5719 BY DISENTANGLING ITS

STELLAR POPULATIONS COUNTER-ROTATIONS

presence of stars/gas counter-rotating with respect to other stars and/or gas

NGC 7217

FEW GAS LOT OF GAS

external origin gas disk built by retrograde acquisitions

internal origin Gas disk built by a bar

Subsequent star formation in the acquired gas disk

FORMATION OF GAS COUNTER-ROTATIONS

1) Acquisition of gas

external origin merger with other galaxies

internal origin secular evolution with disk instability

2) Acquisition of already formed stars and gas

NGC 2855


external origin gas disk built by retrograde acquisitions

internal origin Gas disk built by a bar

Subsequent star formation in the acquired gas disk


1) Acquisition of gas

external origin merger with other galaxies

internal origin secular evolution with disk instability

2) Acquisition of already formed stars and gas

Expected observables

1) Age of the counter-rotating component is younger

2) Age of the counter rotating component younger in the 50% of case

Metallicity of gas and stars possibly different

NGC 5719 – DISENTANGLING THE SPECTRA

Flu

x

wavelength

NGC 5719 TEST CASE…

gas

count-stars

co-stars

NGC 5719 – OBSERVATIONS

VIMOS - VIsible MultiObject Spectrograph @UT3

The integral-field spectroscopic observations in service mode

We used the 0.67 arcsec per fiber resolution

Spectral range 4150–6200 Å with a reciprocal dispersion of 0.54 Å/pixel

The instrumental spectral resolution measured at 5200 Å was 2.0 Å (FWHM)

NGC 5719 – DISENTANGLING THE SPECTRA

NGC 5719 – 2D FIELD kinematic

gas count-stars

co-stars

NGC 5719 – INDICES

NGC 5719 – 2D FIELD STELLAR POPULATION

Age Metallicity A/Fe Co

rota

ting

C

ou

nte

r-Co

rota

ting

NGC 5719 – CONCLUSIONS

5719 is decomposed into the contributions of three distinct kinematic components characterised by a regular disc-like rotation: one main and one secondary stellar component and a ionised-gas component.

The ionised gas is detected all over the observed field of view. It is characterised by a strong Hβ emission, which is concentrated in a twin-peaked morphology indicating an edge-on ring

The contributions of the 2 components to the total light is F(main) = 56% and F(secondary) = 44%

We prove that the mean age of the counter-rotating disc, which is associated to the neutral and ionised gas disc, is indeed younger than the main stellar disc. This result shows that counter-rotating disc has been recently assembled.

The scenario proposed by Vergani et al. (2007) that NGC 5719 hosts a counter-rotating stellar disc originated from the gas accreted during the ongoing merging with its companion NGC 5713, is finally confirmed.

NGC 4550

NGC 3593

NGC 4550, NGC 3593 – STELLAR POPULATIONS

NGC 5719, NGC 3593, NGC 4550 – CONCLUSIONS

NGC 3593 and NGC 4550 host a counter-rotating stellar disk, which rotates in the same direction as the ionized gas, and which is on average less massive, younger, metal poorer, and more α enhanced than the main stellar galaxy disk.

NGC 3593: counter rotating stellar disk is younger than the main disk

NGC 4550: counter rotating stellar disk is younger than the main disk

Our results support the scenario of external gas acquisition, followed by a subsequent outside-in star formation as the origin of the observed counter-rotation.

The merger scenario cannot be completely ruled out, given the low statistics available.

Counterotation – next step

Large survey of the north and south sky to oberve all the galaxy with hints of counter rotations. Candidates for the north are chosen with [email protected] Asiago telescope.

SOUTH NORTH

VIMOS@VLT

VIRUS-P@VLT


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