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The interstellar medium of star-forming dwarfs In Virgo: probing the evolution of low-mass systems in a cluster environment

Marco Grossi - ObservatСrio do Valongo, UFRJ
with the Herschel Virgo Cluster Survey (HeViCS) team

IGM@50, Spineto, 7-12 June, 2015


Objectives
1. Investigate the effects of the environment on the dust component in star-forming dwarf systems.
2. Search for molecular CO emission in FIRdetected SF dwarfs

Evolution of SF dwarfs in a dense environment


The Herschel Virgo cluster survey
P.I: J. Davies

Davies +2012; Auld +2012


Dust in Virgo star-forming dwarfs
·49 out of 140 galaxies classified as Sm, Im, BCD in the optically selected Catalog of the Virgo cluster (Binggeli et al. 1985, 1987). ·43% detection rate considering completeness level of the catalog (mB < 18 mag)

Grossi +2015


Dust in Virgo star-forming dwarfs
·49 out of 140 galaxies classified as Sm, Im, BCD in the optically selected Catalog of the Virgo cluster (Binggeli et al. 1985, 1987). ·43% detection rate considering completeness level of the catalog (mB < 18 mag)

Grossi +2015


Spatial distribution
As expected, dusty SF dwarf galaxies, tend to avoid the densest regions (cluster A and B).


HI mass fractions
Comparison samples HeViCS bright galaxy Catalogue(BGC)
Davies+2012

Average scaling relations for HI-normal and extremely HI-deficient galaxies in H3 survey (Gavazzii+2013)

Dwarf galaxy survey (DGS) Madden+2013 KINGFISH
Kennicutt 2011


Specific star formation rates
Schiminovich +2007

Comparison samples HeViCS bright galaxy Catalogue(BGC)
Davies+2012

Dwarf galaxy survey (DGS) Madden+2013 KINGFISH
Kennicutt 2011


Dust fraction vs stellar mass
Massive galaxies: Dust fraction decreases at higher stellar masses (HRS:Cortese+2012; Bekki+2013; )


Dust fraction vs stellar mass
Massive galaxies: Dust fraction decreases at higher stellar masses Virgo SFDs galaxies: Poor correlation between Md/M* and stellar mass.


Dust fraction vs stellar mass
Massive galaxies: Dust fraction decreases at higher stellar masses Virgo SFDs galaxies: Poor correlation between Md/M* and stellar mass.
SF Active dwarfs: No clear correlation between Md/M* and stellar mass.


Dust fraction vs HI deficiency
The most HI-deficient Virgo galaxies at both High ( ) and low ( ) M* have on average lower dust fractions .
Dust and gas are removed outside-in during the interaction with the intracluster medium as galaxies infall into the cluster (Cortese+12,de
Looze+2013, Gavazzi+2014;


Comparison with transition-type dwarfs

De Looze +2013 Di Serego+2013


Comparison with transition-type dwarfs


Ram-pressure stripping
· The ram pressure stripping exerted by the hot and dense intergalactic medium on dwarf galaxies moving within the cluster is sufficient to fully remove, on very short timescales (~200 Myr; Boselli+2014). · Infalling galaxies stop the star formation activity, and are transformed in red systems in 1 Gyr. The efficiency even increases with multiple crossings of the cluster (Boselli +2008). · As galaxies fall into the cluster the interstellar medium can be retained only in the inner regions, with a higher gravitational potential well (de Looze+2013).


The CO content of FIR-detected Virgo SF dwarf galaxies
~40 hours @ IRAM using the Eight Mixer Receiver (EMIR) Simultaneous observations in two bands E90 ­ E230 looking for CO(1-0) ­> 115 GHz and CO(2-1) ­> 230 GHz lines 8 GHz bandwidth per polarisation. 20 dwarfs observed.
The beam size at 115 and 230 GHz is 22'' and 11'', respectively. 1.8 and 0.9 kpc @ 17 Mpc Herschel/SPIRE beam @ 250 um is 18''.


The sample
SDSS g band SPIRE 250 um


Detections vs non-detections
50% detection rate


Detections vs non-detections
50% detection rate

VCC324

12 + log(O/H) = 8.14 ± 0.1


Scaling relations: H2 mass fraction vs stellar mass
Comparison with Samples of galaxies in different environments: the Herschel Reference Survey (Boselli et al. 2010,2014), a K-band selected sample of 323 galaxies (15

H2 depletion time vs HI deficiency
A moderate H2 deficiency Is observed in the Hi ­ Deficient galaxies of the Herschel Reference Survey (Boselli+14) The extent of the molecular disc decreases with increasing Hi-deficiency in HRS spirals. The molecular component is removed less efficiently than the atomic one in the HRS sample.


Summary
· Dust and gas are removed outside-in during the interaction with the intracluster medium as galaxies infall into the cluster · Extremely HI-deficient star-forming dwarfs show lower dust fractions compared to HI-normal dwarfs. · As galaxies fall into the cluster the interstellar medium can be retained in the inner regions (transition ­type dwarfs). Dust and molecular disks are removed less efficientlt compared to HI.

· HI-deficient spirals appear to be also H2 deficient, however a larger sample of CO-detected dwarfs will be necessary to study environmental effects on the molecular component in SF dwarfs.