JOUNI KAINULAINEN

MASSIMILIANO ESPOSITO

SZYMON KOZLOWSKI

M. ANGELES MARTINEZ CARBALLO

TUTOR: ANNA PASQUALI

STAR FORMATION RATE
IN ARP 299

ULIRGs: UltraLuminous
InfraRed Galaxies

ULIRGs are multiple mergers probably descending from Compact Groups of Galaxies (CGG)

LIR> 1012 LSOLAR

As a rule they have tidal tails on large scales, bright star-forming regions and/or dusty AGN's at their centers

They can evolve into elliptical galaxies

Characteristics of ARP 299

IC 694:

SPIRAL GALAXY (Sbr)

AGN IN THE CENTER

MAGNITUDE 16

DISTANCE 41 Mpc

NGC3690:

BARRED SPIRAL GALAXY (SBpec)

HII REGION IN THE CENTER

MAGNITUDE 12

DISTANCE 40.78 Mpc

ARP 299 is an early merger of two gas rich galaxies

IC 694

NGC 3690

Data

46 images retrieved from archive.eso.org

PI names: Maiolino (9726), Malkan (5479), Meurer (6639)

Images were reduced on-the-fly

We selected 14 images for five filters:

Filter F336W (WFPC2) – 4 images (1600 sec)

Filter F439W (WFPC2) – 4 images (920 sec)

Filter F606W (WFPC2) – 1 image (500 sec)

Filter F814W (WFPC2) – 4 images (500 sec)

Filter F160W (NICMOS) – 1 image (120 sec)

Aperture photometry

F160W

F336W

F439W

F814W

F439W

Cosmic rays

F606W

F606W – cleaned

We removed cosmic rays using subroutine L.A.Cosmic

L.A.Cosmic runs under IDL

L.A.Cosmic webpage:

http://www.astro.yale.edu/dokkum/lacosmic

Magnitudes

http://www.stsci.edu/science/starburst99/

Data Analysis

5-band photometry from 17 objects

Model for photometry from Starburst99 (time-series)

Interest: to derive the age and the mass of the star clusters

To do this, we fit the observed photometry to model ----> Age of objects

To revise:

Model gives the de-reddened brightnesses

Observations give the brightnesses that still have intrinsic reddening

---> The intrinsic reddening of objects must also be fitted

Data Analysis – Age and extinction

Color excess E(B-R) is set between 0...5 magnitudes, using the steps of 0.01.

For each E(B-R) and each age, the chi-square is calculated

The smallest chi-square yields the fiducial timepoint and reddening

The intrinsic extinction shifts the cluster from its original position.

Photometry from the Starburst99 forms an evolutionary track

The cluster is shifted back to the track, to a place that corresponds to a certain age

In the color-color diagram:

Data Analysis – Masses

From the Starburst99 we have the brightnesses that correspond to the initial mass setting (106 Mau)

Mass is proportional to luminosity

Extinction values from the fit are used to get the de-reddened magnitude of a cluster

---> The mass of a single cluster is derived by scaling its brightness to the brightness of a model with the same age of the cluster

F = 100.4(Vmodel-Vo)

---> Now we have the mass, and the age. And finally:

SFR = Mass / Age

Data Analysis – Results

Ages: 8 – 18 Myr.

Masses: 105 – 2*107 MAU

SFRMAX = 1.3 MAU yr-1(B2, central object)

This star formation rate is typical for normal galaxies.

The galaxies that are in the middle of the merging process show the SFR:s up to 100-200 MAU yr-1in their central regions.

Conclusions

The fitting of the photometry from the Starburst99 model to the observed brightnesses suggests the typical age of 14 Myr for the star clusters in Arp299.

The derived SFRMAX = 1.3 MAU yr-1 implies, that the interaction between the two galaxies is not powerfull enough to produce high star formation in the inner regions.

Low SFR in Arp 299 implies that the large star formation rate takes place in the very late phase of merging process.

ACKNOWLEDGEMENTS

We would like to thank Anna Pasquali for her endless patience with us :).

We also thank the ESO for the support during these days.

Our work was based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the data archive at the Space Telescope Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

We have made use of the LEDA database (http://leda.univ-lyon1.fr).

We appreciate Pieter G. van Dokkum for delivering the publically available IDL program la_cosmic.pro.

BIBLIOGRAPHY

Alonso Herrero , A. et al.,“ Extreme star formation in the interacting galaxy ARP 299”, 2000 ,ApJ 535, 845-860.

Ballo L. et al.,“ ARP299: a second merging system with two active nuclei?”, 2004,ApJ,600: 634-639.

Genzel, R. et al.,“Ultraluminous infrared mergers: elliptical galaxies in formation?”,2001,ApJ,563, 527-545.

Holtzman, J.A. et al.,”The Photometric Performance and Calibration of WFPC2”,1995, PASP, 107, 1065.

Leitherer, C. et al.,“STARBURST99: synthesis models for galaxies with active star formation”, 1999, ApJS, 123, 3-40.

Pascuali,A. et al.,“ On the formation of star clusters in the merger NGC 6240” ,2003,345,161-174.

Pasquali, A. et al.“Nuclear star formation in NGC 6240” ,2004, A&A, 415, 103-116.

2004-07-21T18:02:16