The star formation history of the local

universe

A/Prof. Andrew Hopkins (AAO)Prof. Joss Bland-Hawthorn (USyd.)

& the GAMA Collaboration

Madusha L.P. GunawardhanaDurham University

DEX X workshop - Durham - 09/01/2014

Evolution of star formation

UV[OII]Hα/Hβsub-mm, radio, FIR & others

Hopkins A.M., 2004, ApJ, 615, 209Hopkins A. M. & Beacom J., 2006, ApJ, 651, 142

★ There are various probes of star formation - Nebula emission lines: [OII], [OIII], Hα, Hβ- Photometric measures: UV, mid-IR, far-IR, radio ★ Each indicator has its advantages and drawbacksUV is a direct tracer of young (>5Mʘ) stars but dust obscured systems are missed in UV samples, making FIR, a tracer of dusty systems, a valuable complementary to UV.

★ There are also survey selection and calibration biases- narrowband vs broadband surveys- flux/magnitude limits- surveys area (cosmic variance)- dust/AGN corrections

★ Covers a wide range in SFR (0.001<SFR(Mʘ yr-1)<100) AND in stellar mass (107<M/Mʘ<1012) AND extends up to z ≈ 0.35

★ The properties of lowest SFR galaxies are investigated in Brough et al. (2011)

Evolution of star formation in Hα

★ Balmer decrement is used to estimate obscuration corrections

SFR vs redshift

Luminosity-dependent obscuration

★ Aperture corrections are based on fibre and Petrosian r-band magnitudes

Hα Luminosity Functions

Gunawardhana et al., 2013, MNRAS, 433, 2764

Schechter vs Saunders functional fits

★ Saunders et al. (1990) function is better suited at fitting the bright-end

of the Hα LF

★ Salim & Lee (2012) also find that the underlying SFR distribution is

better described by a Saunders function than a Schechter function.

Gunawardhana et al., 2013, MNRAS, 433, 2764

Cosmic star formation history

UV[OII]Hα/Hβsub-mm, radio, FIR & others

Hopkins A.M., 2004, ApJ, 615, 209Hopkins A. M. & Beacom J., 2006, ApJ, 651, 142

★ Jurek et al., (2013, MNRAS) find that the bright end of the WiggleZ survey

UV LF is not well described by a Schechter function due to an excess of

UV luminous galaxies.

Local Star Formation History

Gunawardhana et al., 2013, MNRAS, 433, 2764

Bivariate Hα/Mr Distribution

★ For GAMA, the r-band apparent magnitude limit combined with

requirement for Hα detection leads to an incompleteness due to missing

bright Hα sources with faint r-band magnitudes

100 Mʘyr-1

10 Mʘyr-1

1 Mʘyr-1

★ The lowest-z (z<0.1) sample is the most complete with SFRs reaching as

low as 0.001 Mʘ yr-1

Bivariate LHα/Mr Luminosity functions

0.01 Mʘ/yr

0.1 Mʘ/yr

1 Mʘ/yr

100 Mʘ/yr

Gunawardhana et al., (MNRAS, submitted)

Bivariate functional fit vs Copula approach

★ Bivariate functional fit: Ψ(2)(LHα, Mr) = Φ Schechter(Mr) x Φ (LHα, Mr)

★ Bivariate distribution constructed using a Gaussian Copula following the method of

Takeuchi (2010, MNRAS, 406, 1830)

ρ = 0.9

Gunawardhana et al., (MNRAS, submitted)

SFR density plot

SFR density plot

Conclusions★ Star formation in galaxies follows a Saunders (or two-power law) distribution, NOT a Schechter function.

★ GAMA and SDSS Hα luminosity functions confirms this for the first time, making Hα finally consistent with other wavelength estimators of SFR such as IR and radio.

★ Bivariate selection influence ANY star forming sample drawn from a magnitude limited survey. As a consequence the resulting SFRDs are underestimated.

★ One way to correct this is to model the bivariate distribution

★ GAMA website (http://www.gama-survey.org/)

Aperture corrections

★ Aperture corrections are based on fibre and petrosian r-band magnitudes

Aperture correction vs redshift