star forming galaxies

7/27/2019 star forming galaxies

http://slidepdf.com/reader/full/star-forming-galaxies 1/11

Presentation for SAC-2012 on

Observational Studies of Nearby GalaxiesObservational Studies of Nearby Galaxies

Researchers are:Students: Sumit Jaiswal, Chrisphin Karthick (Thesis submitted on 2012)

Faculties: Amitesh Omar, B. B. Sanwal (till 2010)

Research is carried out on topics:1. Star formation in galaxies

2. Triggering mechanism for star formation

Emphasis is on Wolf-rayet galaxies.

Multiwavelength Data are taken using:Radio (HI 21cm-line) data: GMRT

Optical Photometric data: IGO telescope, ARIES telescopes (1.04m-ST & 1.3m-

DFOT), HCT

Optical Spectroscopic data: IGO telescope, HCT



Wolf-Rayet Galaxies ?

Galaxy having sufficient raw material for star formation can undergo to starburst phase with

some triggering mechanism.

It is well known that Galaxy-Galaxy Tidal Interaction can trigger Starburst.

But the reverse statement is not always true, since some starburst galaxies are found to be

non-interacting in their optical images.

If starburst is quite old, then the features of tidal interaction may disappear.

We have to study therefore the galaxies having recent (< 10 Myr) starburst i.e. Wolf – Rayet

Galaxies.

WR galaxies are short lived (a few Myr) phase

in galaxies because of presence of large

number of short lived (≤ 0.5 Myr) WR stars.

Hence, WR galaxies offer an opportunity to

study the onset of star formation and

conditions which may be driving the star

formation in galaxies.

Spectrum of HII region -014+081 in NGC 4254



Work done by Chrisphin & B.B.Sanwal

A detailed photometric (in UBVRI and Hα filters) and optical spectroscopic study of a

sample of 7 WR galaxies, namely, NGC 1140, IRAS 07164+5301, NGC 3738, UM

311, NGC 4861, and NGC 3003.

Star-forming regions within these galaxies have been identified using their Hα

images.



In galaxies NGC 1140, UM 311, NGC 4861 and NGC 3003, the features of recent

interactions are found.



From photometric data, the morphologies, colours, star formation rates, age of starburst and

stellar populations have been estimated.

The optical spectra of the star-forming regions have been used to derive the number of WR

stars, chemical abundances and internal extinctions in these regions.

Spectrum of central region of the galaxy NGC 6764



Work done by Sumit & AmiteshThe main aim of this study is to trace features in optical and radio images indicating the trigger

mechanism of massive star formation in these galaxies.

A survey of about 20 WR galaxies in the HI 21cm-line using GMRT and in Hα-line using 1.3-mDevasthal Optical telescope & 2-m IGO telescope is being carried out.

The galaxy sample includes the compact galaxies not showing highly disturbed morphology or

tidal tails and large galaxies not showing nuclear star formation in their SDSS images.

R-band and Hα images of Mrk 996 from 1.3m-DFOT



As HI envelop is much bigger than the optical envelop, HI-line is the best tracer for tidal

interactions in galaxies.

If tidal features in HI are not detected, it will indicate a strong consideration of other possible

mechanisms of star formation trigger in galaxies.

As Hα emission is a very good tracer of HII regions, the Hα images therefore show how starformation regions are distributed within their host galaxies with respect to the environmental

effects.

The first results on this observational program are very encouraging. We have traced the

features of tidal interaction in few galaxies (e.g., Mrk 996, Mrk 005) which were previously cited

as non-interacting systems.

UGCA 116



HI Channel Maps of Mrk 996

The different channel

images are due to

galaxy rotation.

The long weak

emissions may bedue to tidal tail.



HI Channel Maps of Mrk 005

These weak HI emissionsmay be due to Tidal tail.

HI emissions due

to galaxy rotation.



Hα – Contour Plot

Misaligned Hα (red) and r-disks (green)

Hα contours overlying on r-band contours of Mrk 996,observations taken from 1.3m-Devasthal Telescope

Hα flux = (144 ± 10) × 10−14

erg s−1 cm−2



Papers (in preparation):

1) Evidence of tidal interaction in Wolf-Rayet galaxy Mrk 996

2) 1.3 meter Devasthal Fast Optical Telescope observation of a Wolf-Rayet Galaxy Mrk 996

Conference Abstracts:

1) Photometric and spectrophotometric studies on Wolf-Rayet Galaxies, Chrisphin, K.; Sanwal,

B. B.; Sahu, D. K. & Singh, M., BASI, ASI conf. Proc. 2007, 25, 66

2) GMRT HI imaging of Wolf-Rayet galaxies, Amitesh Omar & Sumit Jaiswal, BASI, ASI conf.

Proc. 2011, 3, 150

Ph.D.s:

1) Study on Star Forming Regions in Wolf Rayet Galaxies (submitted) ---> Chrisphin Karthick

2) Studies of Nearby Star Forming Galaxies (going on) ---> Sumit Jaiswal

Documents

star forming galaxies