Evidence for Outflows in Rest-UV Spectra of z~1-2 ULIRGs

The VISTA Hemisphere Survey (VHS)

Manda Banerji (IoA, Cambridge)

Evidence for Outflows in Rest-UV Spectra of z~1-2

ULIRGs

Manda Banerji (IoA, Cambridge)

Scott Chapman (IoA), Ian Smail (Durham), Susie Alaghband-Zadeh (IoA), Mark Swinbank (Durham), Jim Dunlop (Edinburgh), Rob Ivison (Edinburgh), Andrew

Blain (Leicester)

FIR2011Manda Banerji

Outline• Use rest-UV spectroscopy to trace “cool” ISM in

z~1-2 sub-mm galaxies (SMGs) and sub-mm faint radio galaxies (SFRGs) via various absorption lines

• Already successfully done for low-z ULIRGs (Martin et al. 2005, 2006) as well as optically selected SF galaxies at z~1-2 (Weiner et al. 2009)

• Look for dependence of outflow velocity on different galaxy properties e.g. SFR, stellar mass


Key Questions• How do SMG/SFRGs at z~1-2

compare to lower redshift LIRGs and ULIRGs?

• How do they compare to optically selected star-forming galaxies at similar redshifts?


Sample• 19 SMGs (>5mJy at 850 micron) and 21 SFRGs

(<5mJy at 850 micron) with KeckII-DEIMOS spectra. All have robust radio IDs.– [OII] + various combinations of [NeV], [NeIII], Hδ, Ca K&H for

redshifts– Predominantly MgII and FeII trace cool ISM

• Redshift range – 0.7 – 1.7 – median of 1.3

• Average bolometric luminosity of ~1×1012 L-> average SFR of ~100-200 M/yr


Comparison to optical SF galaxies

Weiner et al. (2009)


Banerji et al. (2011)

Comparison to Previous Studies of SMGs/SFRGs

z~1.3 SMGs/SFRGs (Banerji et al. 2011) fill in the redshift desert in previous spectroscopic studies (Chapman et al. 2004,2005) while also probing a lower luminosity population.


Galaxy Properties – IStar Formation Rates and Dynamical

MassesLarge star formation rates of a few hundred solar masses per year (though considerably less than z~2 SMGs/SFRGs)

Large nebular linewidths corresponding to large dynamical masses.


Optical


Galaxy Properties – IIStellar Masses

Median Stellar Mass

Reference

z~1.3 SMGs (SED fitting)

(3±0.2)×1010 M Banerji et al. (2011)

z~1.3 SFRGs (SED fitting)

(6±0.8)×1010 M Banerji et al. (2011)

z~1.3 SMGs (constant M/L)

(4±0.2)×1010 M Banerji et al. (2011)

z~1.3 SFRGs (constant M/L)

(2±0.2)×1010 M Banerji et al. (2011)

z~2 SMGs (Photo-z) (9±0.9)×1010 M Wardlow et al. (2011)

z~2 SMGs (Spec-z) (7±1.0)×1010 M Hainline et al. (2011)



Median Stellar Mass

Reference


(3±0.2)×1010 M Banerji et al. (2011)


(6±0.8)×1010 M Banerji et al. (2011)


(4±0.2)×1010 M Banerji et al. (2011)


(2±0.2)×1010 M Banerji et al. (2011)



Large scatter in stellar mass estimates due to degeneracies between stellar mass, SFH and dust extinction in SED fits.



Median Stellar Mass

Reference


(3±0.2)×1010 M Banerji et al. (2011)


(6±0.8)×1010 M Banerji et al. (2011)


(4±0.2)×1010 M Banerji et al. (2011)


(2±0.2)×1010 M Banerji et al. (2011)



Evidence that z~1.3 SMGs have smaller stellar masses than those at z~2 ??


Individual Spectra

Typical spectrum has a continuum S/N of ~1.7. Although [OII] is detected at high significance in all cases -> redshifts, studies of absorption features impossible



Stacked SpectrumFIR2011Manda Banerji

Various FeII (2344,2374,2383,2600) and MgII (2796,2803) show up prominently in stacked spectra. Can measure their velocity relative to [OII]


Outflows

OII redshift

MgII terminal

MgII centroid


Doublet is clearly blueshifted


Outflows

OII redshift

MgII terminal

MgII centroid


Count pixels between -500 and -100 km/s to determine centroid


Outflows

OII redshift

MgII terminal

MgII centroid


Centroid velocity -240±50 km/s


Outflows

OII redshift

MgII terminal

MgII centroid


Count pixels between 90-100% of cont to determine terminal v


Outflows

OII redshift

MgII terminal

MgII centroid


Terminal v: -540±100 km/s


Outflow Velocity & Stellar Mass

No significant trend seen and the outflow velocities are consistent with optically selected star-forming galaxies at similar redshifts from Weiner et al. (2009)


Outflow Velocity and SFRFIR2011Manda Banerji

Local LIRGs/ULIRGs

AGN ULIRGs with very large velocities



No evidence for difference in outflow v between AGN and SB and AGN SMGs/SFRGs consistent with local SBs rather than local AGN ULIRGs


Local relation after correcting for projection effects

Momentum-driven wind model from Martin et al. (2006)


Slight increase in v with SFR but both high and low SFR samples are consistent with local relation and momentum-driven wind model


Local relation V α SFR0.3 after correcting for projection effects

Momentum-driven wind model from Martin et al. (2006)

Conclusions• Redshift 1.3 SMGs/SFRGs significantly less luminous

with lower SFRs than those selected at redshift 2• Typical outflow velocities of -240 km/s as traced by

MgII and FeII ions relative to [OII]• AGN and SB dominated galaxies have similar outflows• Slight increase seen in outflow velocity with SFR• Outflows similar to optically selected star-forming

galaxies of similar stellar mass at the same redshifts• Outflows indistinguishable from local LIRGs/ULIRGs


Prospects for Herschel• AGN and SB dominated galaxies driving similar

velocity winds.


• Herschel observations will help confirm the above

• Suggests that radiative pressure from AGN doesn’t accelerate winds and/or starburst is as bolometrically important as AGN

Prospects for ALMA• Low ionisation gas outflows of around -200-300

km/s seen in SMGs and SFRGs at z~1.3


• P-Cygni profiles in molecular lines from Arp220 (Sakamoto et al. 2009) – Molecular Outflows.

• Predicted in high-z ULIRGs by theoretical simulations (Narayanan et al. 2008) • How do molecular outflows compare to rest-UV ionised gas outflows?

Documents

Evidence for Outflows in Rest-UV Spectra of z~1-2 ULIRGs