Differences between CO- and calcium triplet-derived velocity dispersions in spiral galaxies: evidence for central star formation?
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2015Metadata
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Riffel, Rogemar A.
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Differences between CO- and calcium triplet-derived velocity dispersions in spiral galaxies: evidence for central star formation?
Author
- Riffel, Rogemar A.;
- Ho, Luis;
- Mason, Rachel;
- Rodríguez Ardila, Alberto;
- Martins, Lucimara;
- Riffel, Rogerio;
- Diaz, Ruben;
- Colina, Luis;
- Alonso-Herrero, Almudena;
- Flohic, Helene;
- González, Omaira;
- Lira Teillery, Paulina;
- McDermid, Richard;
- Ramos Almeida, Cristina;
- Schiavon, Ricardo;
- Thanjavur, Karun;
- Ruschel-Dutra, Daniel;
- Winge, Claudia;
- Perlman, Eric;
Abstract
We examine the stellar velocity dispersions (σ) of a sample of 48 galaxies, 35 of which are
spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared
galaxies (ULIRGs) and merger remnants, the σ derived from the near-infrared CO band
heads is smaller than that measured from optical lines, while no discrepancy between these
measurements is found for early-type galaxies. No such studies are available for spiral galaxies
– the subject of this paper. We used cross-dispersed spectroscopic data obtained with the
Gemini Near-Infrared Spectrograph, with spectral coverage from 0.85 to 2.5 µm, to obtain
σ measurements from the 2.29 µm CO band heads (σ CO) and the 0.85 µm calcium triplet
(σ CaT). For the spiral galaxies in the sample, we found that σ CO is smaller than σ CaT, with a
mean fractional difference of 14.3 per cent. The best fit to the data is given by σopt = (46.0 ±
18.1) + (0.85 ± 0.12)σ CO. This ‘σ-discrepancy’ may be related to the presence of warm dust,
as suggested by a slight correlation between the discrepancy and the infrared luminosity. This
is consistent with studies that have found no σ-discrepancy in dust-poor early-type galaxies,
and a much larger discrepancy in dusty merger remnants and ULIRGs. That σ CO is lower than
σopt may also indicate the presence of a dynamically cold stellar population component. This
would agree with the spatial correspondence between low-σ CO and young/intermediate-age
stellar populations that has been observed in spatially resolved spectroscopy of a handful of
galaxies.
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MNRAS 446, 2823–2836 (2015)
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