thijs van der hulst kapteyn astronomical institute ... · galaxy evolution over five decades,...

Galaxy Evolution Over Five Decades, Cambridge 3 - 6 September 2013

Thijs van der Hulst

Kapteyn Astronomical InstituteUniversity of Groningen

Galaxies in Voids:special or not?

and the Void Gang:

Kathryn Kreckel (Heidelberg), Burcu Beygu (Groningen), Rien van de Weygaert (Groningen), Jacqueline van Gorkom (New York), Miguel Aragon Calvo (Baltimore), Tom Jarrett (Cape Town), Reynier Peletier (Groningen), ...

Sunday, October 6, 2013


Thijs van der Hulst

Kapteyn Astronomical InstituteUniversity of Groningen

Galaxies in Voids:special of not?

and the Void Gang:

Kathryn Kreckel (Heidelberg), Burcu Beygu (Groningen), Rien van de Weygaert (Groningen), Jacqueline van Gorkom (New York), Miguel Aragon Calvo (Baltimore), Tom Jarrett (Cape Town), Reynier Peletier (Groningen), ...



Why Voids?



- Voids are the most empty regions in the universe

- Voids do still have fine structure: filaments, walls

- Voids evolve and merge

- Substructure in voids expected to form galaxies

- Expect galaxies to evolve ‘quietly’, no harrasment

distribution of local galaxies from SDSS

but: finding voids is not trivial !


Different void finders give different results:



Geometric void selectionDTFE (Schaap & van de Weygaert 2000) plus Watershed Void Finder (Platen et al. 2007)


•  red gals., g-r > 0.6 •  blue gals., g-r < 0.6

the galaxy environment of VGS_58, selected from SDSS

An example: VGS_58



- multiwavelength survey of 60 void galaxies SDSS u, g, r, i, z; deep B imaging, Halpha imaging GALEX NUV, Spitzer 3.6 and 4.5 micron, WSRT HI

- probe morphology, gas content, star formation properties, stellar masses, colours, etc.

- voids selected using pure geometrical methods- galaxies and voids selected from SDSS DR7- no a priori assumption about the shape of the voids- no a priori assumption about the scale of the voids- galaxy selection independent of their properties

The Void Galaxy Survey (Kreckel et al. AJ 144, 16, 2012)



● Void galaxies are blue (Grogin & Geller 1999, Rojas et al. 2004, Croton et al. 2005).

● They have high SFR (Grogin & Geller 1999, Rojas et al. 2004, Gonzales & Padilla 2009).

● They have mostly late – type morphologies (Dressler 1980, Postman& Geller 1984, Croton et al. 2005, Hoyle et al. 2005).

● Their stellar population is young (Grogin & Geller 2000, Kauffmann et al. 2004, Rojas et al. 2005).

● They have low stellar mass (Croton et al. 2005, Goldberg et al. 2005).

Previous results on Void galaxies



HI results

- 41 detections and 14 non-detections - HI mass range 2 x 107 to 6 x 109 Msun

- mostly small disk galaxies, three early type galaxies- many have signs of interactions, asymmetries- HI contents are normal- stellar masses all less than 3 x 1010 Msun

Kreckel et al. AJ 144, 16, 2012



ALFALFA galaxies at δ + 1 < 1Void galaxies

HI contentcomparison with control sample from ALFALFA

selected to be at densities δ + 1 < 10

Kreckel et al. AJ 144, 16, 2012



Remarkable galaxiesVGS _ 12

Huge polar disk in thin wall: accretion in action from the neighbouring voids?

Interacting group inside a void, aligned along LSS filament?

Galaxies not very different from galaxies elsewhere: but have systematically small stellar mass

VGS_31(Stanonik et al. 2009)

(Beygu et al. 2013)

(Kreckel et al. 2012)



- MDM Halpha imaging, GALEX NUV, Spitzer 3.6 and 4.5 micron- stellar masses from MPA-JHU catalog based on SDSS- HI masses from WSRT 21cm imaging

Examine: Star Formation Rate Specific Star Formation Rate Star Formation efficiency

- comparison samples: Halpha survey of galaxies from ALFALFA (Gavazzi et al 2013) Local Volume galaxies (Karachentsev et al. 2013) JCMT field galaxies (Sanchez - Gallego et al. 2012)

Star Formation properties (Beygu et al. in preparation)



Star Formation Efficiency and Specific SFR



Conclusions

- void galaxies very similar to galaxies in other, moderate density environments

- local environment more important than global environment?

- void galaxies are in general small disks

- SF properties normal, except for a few high HI mass systems

work in progress: stay tuned


thijs van der hulst kapteyn astronomical institute ... · galaxy evolution over five decades,...

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