slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Star Formation in Extremely Faint Gas Rich Dwarf Galaxies PowerPoint Presentation
Download Presentation
Star Formation in Extremely Faint Gas Rich Dwarf Galaxies

Loading in 2 Seconds...

play fullscreen
1 / 31

Star Formation in Extremely Faint Gas Rich Dwarf Galaxies - PowerPoint PPT Presentation


  • 155 Views
  • Uploaded on

Star Formation in Extremely Faint Gas Rich Dwarf Galaxies. Ayesha Begum (UW, Madison). Sambit Roychowdhury (NCRA), Jayaram N. Chengalur ( NCRA ), Igor D. Karachentsev (SAO ), Margarita Sharina (SAO). Topics to be addressed.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Star Formation in Extremely Faint Gas Rich Dwarf Galaxies' - ayita


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Star Formation in Extremely Faint Gas

Rich Dwarf Galaxies

Ayesha Begum (UW, Madison)

SambitRoychowdhury (NCRA), JayaramN. Chengalur(NCRA),

Igor D. Karachentsev (SAO), Margarita Sharina (SAO)

topics to be addressed
Topics to be addressed
  • What factors govern star formation in faint gas rich dwarf galaxies ?

☛ Dwarf galaxies are dynamically much “simpler” systems

compared to bright galaxies  Ideal to study the

interplay between neutral ISM and star formation.

  • Baryon fraction in faint gas rich dwarf galaxies

☛Theory/numerical simulations vs observations

f aint i rregular g alaxies g mrt s urvey figgs
Faint Irregular Galaxies GMRT Survey (FIGGS)
  • A survey of the neutral hydrogen (HI) emission in a large sample (~65) of nearby (< 10 Mpc), faint (MB>-14.5) dwarf irregular galaxies with the GMRT

The faintest sample galaxies ~ 104 times less luminous than typical L* galaxy

  • Obtain high-quality observations of atomic ISM at high velocity resolution (~1.6 km/s) and variety of spatial resolutions (~ 40” – 5”)
  • FIGGS Sample
    • Median MHI ~ 3 X 107Msun, MB ~ -13.0 mag ,

HI flux > 1.0 Jy km/s

  • 65 galaxies with GMRT HI cubes, optical broad band and Ha images
    • Sub samples with TRGB distances, optical spectroscopy, GALEX images,…
giant metrewave radio telescope
Giant Metrewave Radio Telescope

■GMRT is an interferometric array

consisting of 30 antennas, each of 45 m

diameter, spread over 25 km region in a

hybrid (Y shaped configuration), 90 km off

Pune in India

  • Operating frequencies are 1420, 610, 327,

233 and 150 MHz

14 Dishes in compact array

14 dishes in a

compact array

f aint i rregular g alaxies g mrt s urvey figgs1
Faint Irregular Galaxies GMRT Survey (FIGGS)
  • A survey of the neutral hydrogen (HI) emission in a large sample (~65) of nearby (< 10 Mpc), faint (MB>-14.5) dwarf irregular galaxies with the GMRT

The faintest sample galaxies ~ 104 times less luminous than typical L* galaxy

  • Obtain high-quality observations of atomic ISM at high velocity resolution (~1.6 km/s) and variety of spatial resolutions (~ 40” – 5”)
  • FIGGS Sample
    • Median MHI ~ 3 X 107Msun, MB ~ -13.0 mag ,

HI flux > 1.0 Jy km/s

  • 65 galaxies with GMRT HI cubes, optical broad band and Ha images
    • Sub samples with TRGB distances, optical spectroscopy, GALEX images,…
gas fraction of figgs galaxies
Gas Fraction of FIGGS Galaxies

►Average gas fraction of FIGGS galaxies < fgas >~ 0.7

► Trend of increasing gas fraction with a decrease in luminosity/mass

 FIGGS probe the regime of faintest, very low mass, gas rich galaxies

► Extending the baseline for a comparative study of galaxy properties

Gas Fractionfgas= Mgas/(Mgas+Mstar)

Begum et al. 2008a,MNRAS,386,1887

extended hi disks of figgs galaxies
Extended HI disks of FIGGS galaxies

DHI (1 X 1019 cm-2)

DHo (26.5 mag arcsec-2)

DHI/DHo

►Average HI extent of FIGGS galaxies ~ 2.7 times Holmberg radii

► Discovery of extremely extended HI disks around galaxies.

Begum et al. 2008a,MNRAS,386,1887

ngc 3741 m b 13 0 mag
NGC 3741 (MB ~ -13.0 mag)

Dwarf Galaxies with Giant HI Disks

HI disk extends to 8.8 times the Holmberg radius

MD/LB ~ 107

NGC 3741 Galaxy with the most extended HI disk

 A unique opportunity to trace the large scale mass distribution

around dwarf galaxies

Begum et al. 2008b, MNRAS 383, 809, Begum et al. 2005, A&A, 433, 1L

slide9

Dwarf Galaxies with Giant HI Disks

And IV (MB ~ -12.4 mag)

HI extends to ~ 7 times Holmberg radius

Vrot (km/s)

Radius (kpc)

MD/LB~ 237  One of the “darkest irregular galaxies known

Do “dark” galaxies have anomalously low baryon fractions?

baryon fraction in numerical simulations
Baryon fraction in numerical simulations
  • Small halos are less efficient at capturing baryons
    • Hot baryons escape during the epoch of reionization
    • Feed back from star formation drives baryons out of shallow dwarf galaxy potential wells
  • Baryon fraction expected to vary inversely with galaxy mass

(Gnedin, 2000, ApJ, 542, 533;

Hoeft et al. 2006, MNRAS, 371, 401)

Data from Hoeft et al. 2006, MNRAS, 371, 401

baryon fraction in gas rich galaxies
Baryon fraction in gas rich galaxies

Begum et al. 2009

  • Large scatter in baryon fraction for all galaxies
  • Dwarf galaxies don’t have systematically smaller baryon fractions
  • AndIVand N3741 do have less than the average cosmic baryon fraction – but so do many other galaxies

Cosmic baryon fraction

Baryon fraction in galaxies with well measured HI rotation curves

star formation in dwarf galaxies
Star formation in dwarf galaxies

★Bright spiral galaxies

► Star formation rate correlated to the gas column density

(Kennicutt -Schmidt power-law relation)

► Suppression of star formation below critical column density

(Tomre's instability criterion)

★ Nature of process regulating star formation in dwarf galaxies poorly understood

★ Number of extremely faint dIrr galaxies studied is too small to make any definite conclusions

★ Stochasticity in the Hα based SFR for extremely faint dwarf galaxies

(Oey & Clarke, 2005)

UV a better tracer of SF in faint dwarf galaxies

star formation in figgs galaxies using hi and uv
Star formation in FIGGS galaxies using HI and UV

■ Sample of 23 FIGGS galaxies with publicly available GALEX data

Study of globally averaged and “pixel-to-pixel” correlation

between SF and HI in each of these FIGGS galaxies

■ Observed column density resolution dependent

ProducedHI maps corresponding to ~ 400 pc & 200 pc resolution

comparison of hi and fuv emission in figgs galaxies at 400 pc resolution
Comparison of HI and FUV emission in FIGGS Galaxies at ~ 400 pc resolution

Roychowdhury et al. 2009, MNRAS (in press)

global kennicutt schmidt law
“Global” Kennicutt-Schmidt Law
  • FIGGS galaxies haveΣSFR below that predicted by Kennicutt (1998) relation
  • Σgas are around or below the expected “threshold density” (Kennicutt (1989); Martin & Kennicutt (2001)

Slope=-1.4)

Slope=-2.47)

Slope=-1.4

Dwarfs and spirals have a steeper dependence of SFR on the gas densities than predited by KS law

Environmental dependence of star formation efficiency

pixel by pixel comparison of sfr and gas for figgs galaxies at 400 pc resolution
“Pixel by pixel” comparison of ΣSFR and Σgasfor FIGGS galaxies at 400 pc resolution
  • At low Σgas, ΣSFR constant, followed by a power-law increase in ΣSFR with Σgas
  • No evidence for “threshold” density below which the star formation is completely quenched in any galaxy
  • The ΣSFR generally lies below that predicted by Kennicutt relation.
  • At high gas densities, the observed ΣSFR begins to approach the predicted rate
small scale correlation between sfr and gas at 400 pc resolution
Small scale correlation between ΣSFR and Σgasat 400 pc resolution
  • Power law dependence of ΣSFR on Σgas
  • Parameters of the power law fit vary significantly from galaxy to galaxy
  • The index of power law steeper than 1.4 from Kennicutt (1998) relation
  • No evidence for “threshold” density below which the star formation is completely quenched in any galaxy
deviant galaxies
Deviant Galaxies
  • For 5 galaxies, no good power-law parametrization of (ΣSFR ,Σgas) relation
  • Substantial offsets between HI and UV peaks
  • Same galaxies outliers in the “global” (ΣSFR ,Σgas) relation
  • HI masses near the lower end of our sample distribution.
pixel by pixel comparison at 200 pc resolution
Pixel-by-pixel comparison at 200 pc resolution
  • HI and FUV images for 10 galaxies at 200 pc resolution
  • More pronounced offsets between HI and FUV peaks

 Feedback from star formation or molecular gas

  • Power-law parametrization of (ΣSFR, Σgas) for 5/10 galaxies.
  • Similar trend as seen at 400 pc resolution
  • The power law index at 200 pc flatter than at 400 pc resolution
  • Average Σgas higher at 200 pc than 400 pc
conclusions on star formation study in faint galaxies
Conclusions on star formation study in faint galaxies

There is, initially at least, a near universal relation between ΣSFRΣgas.

Feedback and other effects may lead to a breakdown of this relation.

 Dwarfs have a lower star formation efficiency both because sufficiently dense regions are rarer, and affect of feedback is more important

introduction
Introduction

■ Dwarf galaxies form first in hierarchical models

►Dwarfs form building blocks of larger galaxies

■ Study of dwarfs provide a test of various predictions of

hierarchical models

►Shape of dark matter halos, correlations between halo

parameters

■ Dwarf galaxies are dynamically much simpler systems

compared to bright galaxies

►Ideal to study the interplay between neutral ISM

and star formation

ddo 43 14 5 mag
DDO 43 (~ -14.5 mag)

Typical data products from the survey

46” X 42”

33” X 22”

15” X 13”

11” X 10”

46” X 42”

32” X 22”

12” X 10”

6” X 5”

why figgs
Why FIGGS ?

☛ Interplay between neutral gas and star formation in faintest

gas rich galaxies

►Star formation threshold for faint galaxies

☛ Extend the Baryonic Tully-Fisher relation to a regime of very

low mass/luminosity.

☛ Density distribution of dark matter halos

Create archival dataset (calibrated (u,v) data, data cubes, MOMNT maps,

HI spectrum and rotation curves) for the astronomical community.

►Test the predictions on the shape of dark matter halos and

various correlations between halo parameters

ddo 210 m b 10 6 mag

ΔV ~ 1.6 km/s

Begum & Chengalur 2004 A&A, 413, 525

DDO 210 (MB ~ -10.6 mag)

High velocity resolution crucial for the observations of faint dwarf galaxies

Dwarfs fainter than MB ~ -14.0 have chaotic velocity fields ???

(e.g. Cote et al. 2000 AJ 120 3027, Lo et al. 1993 AJ 106 507)

V ~ 6.5 km/s

Lo et al. 1993 AJ, 106, 507

hybrid configuration of gmrt
Hybrid configuration of GMRT

■ 14 antennas located in central compact array

➡ Sensitivity to faint extended

emission

■Rest distributed in Y shaped

configuration with a maximum

baseline of 25 km.

➡ High resolution

14 Dishes in Compact array

➡GMRT’shybrid configuration allows one to make both low resolution (~ 40”)

and high resolution (~ 3”) images from a single observing run

baryon fraction in dwarf galaxies
Baryon fraction in dwarf galaxies
  • Small halos are less efficient at capturing baryons
    • Hot baryons escape during the epoch of reionization
    • Feed back from star formation drives baryons out of shallow dwarf galaxy potential wells
  • Baryon fraction expected to vary inversely with galaxy mass

Gnedin, 2000, ApJ542, 533

baryon fraction theory vs observation
Baryon fraction: Theory vs Observation
  • Since baryons are concentrated at the center of the halo the baryon fraction increases with decreasing radius
  • Simulations give baryon fraction at the virial radius
      • Observations determine the baryon fraction up to the last measured point of the rotation curve
  • Simulations suggest that the baryon fraction within the last measured point of the rotation curve should vary inversely with halo mass

Data from Hoeft et al. 2006, MNRAS, 371, 401