The role of cold gas in the chemical evolution of nearby galaxies

Transcription

1 The Role of Hydrogen in the Evolution of Galaxies Kuching, 17 th September 2014 The role of cold gas in the chemical evolution of nearby galaxies Tom Hughes Luca Cortese (Swinburne), Alessandro Boselli (LAM), Guiseppe Gavazzi (Milan), Jonathan Davies (Cardiff), Veronique Buat (LAM)

2 The baryonic matter cycle INTERGALACTIC MEDIUM Gas cools in the ISM, aided by dust Stars form in collapsing gas clouds Dust forms in cooling metal rich gas Expulsion of metals & unprocessed gas Metals from stellar nucleosynthesis

3 Mass Oxygen abundance Stellar mass metallicity Lequeaux et al Tremonti et al >53,000 SDSS galaxies Metallicity Stellar mass

4 Dave et al Some open questions Shape - galactic scale winds - variable SF efficiency - variable IMF Conserved Constant No wind Slow

5 Tremonti et al Some open questions Shape - galactic scale winds - variable SF efficiency - variable IMF Scatter - most galaxy properties do not correlate with metallicity residuals Mass Surface density Concentration Inclination Colour Ha EW

6 Mouhcine et al Skillman et al Some open questions Shape - galactic scale winds - variable SF efficiency - variable IMF Scatter - most galaxy properties do not correlate with metallicity residuals Environment - weak/strong dependence (see e.g. Cooper et al 2008) - no statistical dependence B magnitude V Circ Hubble Type (see e.g. Ellison et al 2008) Local density Local density

7 Skillman et al.1996 Role of gas content Predict: decreasing Z with increasing gas fraction μ: Z = y ln (1 / μ) (Edmunds 2001) Observe: in Virgo. Infer: K-S Law (Tremonti et al. 2004), HI Scaling relations (Zhang et al. 2009).

8 Herschel Reference Survey - magnitude- and volume-limited sample covering 323 nearby galaxies in a range of environments, from isolated systems to Virgo cluster members (Boselli et al. 2010). Sample selection criteria: Mpc volume limit 2MASS K stot 12 mag Galactic latitude > +55º Extinction A B < 0.2 Ancillary data is complete for: H, B & V photometry ~ stellar mass NUV GALEX imaging ~ SFR HI 21cm ~ HI gas mass Drift-scan spectra ~ metallicity

9 Herschel Reference Survey - magnitude- and volume-limited sample covering 323 nearby galaxies in a range of environments, from isolated systems to Virgo cluster members (Boselli et al. 2010). Sample selection criteria: Mpc volume limit 2MASS K stot 12 mag Galactic latitude > +55º Extinction A B < 0.2 Ancillary data is complete for: H, B & V photometry ~ stellar mass NUV GALEX imaging ~ SFR HI 21cm ~ HI gas mass Drift-scan spectra ~ metallicity Error-weighted mean oxygen abundance from combination of strong-line metallicity calibrations and base conversions from Kewley & Ellison (2008).

10 Residual abundance Hughes et al Oxygen abundance Observed role of hydrogen HI deficiency is: the difference between the observed HI mass and that expected for an isolated galaxy of similar size and type. Blue circles Galaxies with normal gas content Red circles Gas deficient objects, i.e. galaxies missing up to 70% of their gas compared to healthy isolated systems. Log stellar mass (Gas-poor Gas fraction Gas-rich) Scatter in M-Z relation correlates with gas fraction. Gas-deficient objects typically more metal-rich.

11 Residual abundance Hughes et al Oxygen abundance Effects of environment Log stellar mass Log Gas stellar fraction mass Log stellar mass No significant environmental dependence, consistent with Ellison et al Mouhcine et al. 2007

12 Residual abundance Hughes et al Oxygen abundance Effects of environment Log stellar mass Log stellar mass Log stellar mass HI-deficient select systems most perturbed by environment, also consistent with Skillman et al. 1996, Gavazzi et al 2004.

13 Chung et al, 2007 Hughes et al An observational bias? Drift scan spectroscopy only probes metallicity across observable HII regions NGC 4254 metallicity profile (Skillman et al. 1996) Degeneracy only broken using IFU spectroscopy (e.g. SAMI, CALIFA, MaNGA)

14 Oxygen abundance Mannucci et al Oxygen abundance M-Z-SFR relation Does SFR govern scatter? - a fundamental M-Z-SFR (see e.g. Lara-Lopez et al. 2010, Mannucci et al. 2010) Log Mass

15 Residual abundance Sanchez et al Residual abundance M-Z-SFR relation Does SFR govern scatter? - a fundamental M-Z-SFR (see e.g. Lara-Lopez et al. 2010, Mannucci et al. 2010) Integrated HII regions CALIFA results - correlation between SFR and scatter only found when simulating SDSS apertures (Sanzhez et al. 2013) Log SFR Log μsfr Simulated SDSS apertures Log SFR

16 Residual abundance Sanchez et al Residual abundance M-Z-SFR relation Does SFR govern scatter? - a fundamental M-Z-SFR (see e.g. Lara-Lopez et al. 2010, Mannucci et al. 2010) Integrated HII regions CALIFA results - correlation between SFR and scatter only found when simulating SDSS apertures (Sanzhez et al. 2013) Log SFR Log μsfr Simulated SDSS apertures Independent studies - HI content drives scatter (see e.g. our work; Bothwell et al. 2013) - SFR a proxy for gas content (see e.g. Kahid et al. 2014) Log SFR

17 Summary First time combined direct gas information with metallicities from drift-scan optical spectroscopy using new calibration techniques. Gas content related to scatter of M-Z relation, environment of secondary importance. Future work must examine the spatially-resolved observations to avoid potential aperture biases. See Hughes, Cortese et al., 2013, A&A, 550, 115H Boselli, Hughes et al., 2013, A&A, 550, 114B