[Paper Review] The Herschel Virgo Cluster Survey. XVIII. Star-forming dwarf galaxies in a cluster environment

M. Grossi, L. K. Hunt+23 more|Research Explorer (The University of Manchester)|Nov 14, 2014

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy198 references20 citations

TL;DR

This study analyzes far-infrared and submillimeter properties of 140 star-forming dwarf galaxies in the Virgo cluster using Herschel data to assess environmental effects on dust, gas, and star formation. It finds that while H i gas is preferentially stripped, dust is less affected, implying longer timescales for dust removal and suggesting that cluster environments primarily quench star formation via gas stripping rather than dust destruction.

ABSTRACT

To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the FIR-submm properties of a sample of star-forming dwarf (SFD) galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body (MBB) function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than $m_B$ = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by $β$=1.5, with a median dust temperature $T_d$ = 22.4 K. Assuming $β$=1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 $μ$m in excess of the MBB model. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample due to environmental effects, we compare the Virgo SFDs to other Herschel surveys, such as KINGFISH, the Dwarf Galaxy Survey (DGS), and the HeViCS bright galaxy catalogue (BGC). We explore the relations between stellar mass and HI fraction, specific SFR, dust fraction, gas-to-dust ratio over a wide range of stellar masses. Highly HI-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, we find that the fraction of dust removed has to be less than that of the HI component. Since the Virgo SFDs are likely to be crossing the cluster for the first time, a longer timescale might be necessary to strip the more centrally concentrated dust distribution.

Motivation & Objective

• To investigate how the dense cluster environment of Virgo affects the interstellar medium components—dust, gas, and star formation—across a sample of star-forming dwarf galaxies.
• To determine dust masses and temperatures via modified blackbody fitting to spectral energy distributions (SEDs) in the far-IR and submillimeter bands.
• To compare the properties of Virgo dwarfs with those from other Herschel surveys (KINGFISH, DGS, HeViCS BGC) to isolate environmental effects on stellar mass, gas fraction, dust fraction, and star formation rate.
• To assess the relative stripping efficiency of dust versus H i gas in cluster dwarfs, particularly in highly H i-deficient systems.
• To explore the implications of observed dust-to-gas ratios for dust removal mechanisms and the evolutionary timescales of dwarfs entering the cluster for the first time.

Proposed method

• Spectral energy distributions (SEDs) of 140 optically identified star-forming dwarfs in the HeViCS field were fitted with a modified blackbody function to derive dust masses and temperatures.
• Emissivity index β was evaluated across multiple values, with β = 1.5 found to best fit the FIR-submm SEDs, yielding a median dust temperature of 22.4 K.
• Submillimeter excess at 500 μm was quantified by comparing observed SEDs to model predictions, with 67% of 23 galaxies detected in all five Herschel bands showing excess emission.
• Ancillary data (optical, radio, ALMA, IR) were used to derive stellar masses, gas masses, star formation rates (SFRs), and metallicities.
• Environmental effects were assessed by comparing the Virgo dwarf sample to external surveys (KINGFISH, DGS, HeViCS BGC) across a wide stellar mass range (10⁷–10¹¹ M⊙).
• Relations between stellar mass, H i fraction, specific star formation rate (sSFR), dust fraction, and gas-to-dust ratio were analyzed to identify deviations due to cluster environment.

Experimental results

Research questions

• RQ1 How does the cluster environment of Virgo affect the dust content and temperature in star-forming dwarf galaxies?
• RQ2 What is the relative stripping efficiency of dust versus H i gas in cluster dwarfs, and what does this imply about the timescales of environmental transformation?
• RQ3 Why do highly H i-deficient dwarfs still exhibit relatively high dust-to-gas ratios despite significant gas loss?
• RQ4 How do the dust and gas properties of Virgo dwarfs compare to those of similar galaxies in less dense environments?
• RQ5 What role does the initial state of the dwarf (e.g., first-time cluster entry) play in the observed environmental effects on star formation and ISM components?

Key findings

• Dust was detected in 49 out of 140 optically identified dwarfs, with a detection rate of 43% for galaxies brighter than m_B = 18 mag.
• The FIR-submm SEDs of the sample are best fit by a modified blackbody with emissivity index β = 1.5 and a median dust temperature of 22.4 K.
• 67% of the 23 galaxies detected in all five Herschel bands show excess emission at 500 μm, indicating a submillimeter excess that is inversely correlated with SFR and stellar mass.
• The submillimeter excess fraction decreases with lower β values, but remains high (54%) when β-free SED modeling is applied, suggesting robustness of the excess detection.
• Highly H i-deficient dwarfs show quenched star formation, lower dust fractions, and reduced H i and dust content, indicating environmental quenching via gas stripping.
• The dust-to-gas mass ratio remains high in H i-deficient systems, implying that dust removal is less efficient than H i stripping, likely due to the more extended H i disks compared to the centrally concentrated dust distribution.