Vandana Desai Spitzer Science Center

with Lee Armus, Colin Borys, Mark Brodwin, Michael Brown, Shane Bussmann, Arjun Dey, Buell Jannuzzi, Emeric Le Floc’h,

Jason Melbourne, Alexandra Pope, Tom Soifer

Dust-Obscured Galaxies (DOGs)

The role of high-z ULIRGs

Merger

Starburst

AGN “on”

Quasar

Massive Galaxy

and their relation to mergers, star formation, AGN, and the formation of massive galaxies

Dey et al. 2009 after Sanders et al. 1988

The z=2 ULIRG zoo

Caitlin’sMIPS-70ULIRGs

Alejo’s Host-obscured

Quasars

SMGs

9 deg9 deg22

Bw, R, I, K ~ 27.1, 26.1, 25.4, 19.0 mag (Vega)Bw, R, I, K ~ 27.1, 26.1, 25.4, 19.0 mag (Vega)MIPS-24 ~0.3 mJyMIPS-24 ~0.3 mJy

PIs: A. Dey & B. Jannuzi

NOAO Deep Wide-Field SurveyGround-based Data for Bootes Field

Dust-Obscured Galaxies (DOGs)

€

R −[24] ≥14

fν (24)

fν (R)≥1000

νfν (24)

νfν (R)≥ 27

Most extreme 10%

R-[24] (Vega mag)

Frac

tion

Redshift

R-[2

4] (V

ega

mag

)DOG Selection

Warning: Need better data on UV emission from local ULIRGs.

Dey+08

Dey +08

DO

G F

racti

on

...where we find the peak of the 24m counts!

increasingly significant numbers at fainter fluxes... Papovich et al. 2004

24 micron flux (mJy)

24 micron flux (mJy)

Papovich +04

24 micron flux (mJy)Eucl

id N

orm

# C

ount

s

The DOG criterion selects for z = 2

Dey+08

LIR = ULIRGs (large error)

Space density = (2.82+-0.05)x10-5h70

Mpc-3

(like 4L* galaxies)

Log(IRLD) = 8.23+0.18

-0.30 Lsun Mpc-3

•60% of all z=2 ULIRGs•25% of IRLD at z = 2

Power Laws and Bumps

Bright

Power-Law

AGN

Faint

“Bump”

starforming

Spectroscopy of Power-Law DOGsHouck+05, also Weedman+06, Yan+06IRS NIRSPEC Brand+07

•7/10 are broad-line AGN•Extinction to narrow and broad-lines high – host obscured?

•AGN-like: •silicate absorption•Weak PAHs

Desai+09, Huang+09, Farrah08

Spitzer/IRS spectra of bump DOGs

NIR spectra of bump DOGs

No NIR spectra of bump sources due to inconvenient redshift.

70 micron selection? Casey+09, Farrah+09Desai+09

Morphology - HST

• Extended emission dominates

• Few on-going mergers

2” Morphologies of power-law DOGs

rest-UV rest-UV rest-opticalrest-optical

Bussmann et al. 2009a;See also Dasyra et al. 2009

Morphology - HST

• On-going interactions more common

• More similar to SMGs (Borys et al., in prep)

2”

Morphologies of bump DOGs

rest-optical

Bussmann et al. 2010, in prep.

Morphology – Keck AO

Melbourne et al. 2009

Fainter (bump/SF) DOGs are more diffuse than bright (PL/AGN) DOGs.

Clustering

Strong clustering

Comparable to SMGs & QSOs

Large uncertaintiesF(24) [mJy]

Brodwin et al. 2008, Magliocchetti+08, Farrah+06

2<z<2.5 QSOs (Shen et al. 2008)1.4<z<2 QSOs (Shen et al. 2008)

2<z<2.5 QSOs (Shen et al. 2008)

R 0 (h-1

Mpc

)

FIR SEDs of PL DOGs5/12 detected at 350m with CSO

0/2 of these detected at 1.3mm with CARMA

Preferred SED:Mrk231

Tdust > 45 K (Warmer than SMGs)

Mdust ~ 3x108 Msun

Bussmann et al. 2009b

FIR SEDs of bump DOGs

Pope+08, see also Lonsdale+09,Fiolet09

PACS 110 mSCUBA-2 450 m

70 faint DOGs in GOODs-N

Stack 70, 160, 850, 1.2mm

TBDOG ~ TSMG

Need some extra hot dust (10% of LIR) compared to SMGs

SFR = 200 Msun/yr

Stacked X-rays consistent with SF, but see Fiore+08

Herschel GTO observations of Bootes5- instrumentaltotal sensitivity (mJy)

110 mPACS

160 mPACS

250 mSPIRE

350 mSPIRE

500 mSPIRE

Level 5 2 deg2 20.4 29.331 1426 19.328 16.326

Level 6 8 deg2 38.2 54.856 26.234 36.141 30.436Herschel probes peak of DOG SED!

Bright, rare Bootes DOGs likely detected in L5 250 m data depending on:• confusion• the power of priors• FIR SEDs

Bulk properties attainable through stacking

Herschel Key Program in GOODS

PACS 110 mSCUBA-2 450 m

PACS and SCUBA-2 will detect most (fainter) DOGs in GOODs.

Pope et al. 2008

The role of high-z ULIRGs

Merger

SMG – bump DOG

PL DOG

Quasar

Massive Galaxy

and their relation to mergers, star formation, AGN, and the formation of massive galaxies

Dey et al. 2009 after Sanders et al. 1988

Summary• ~Half of z = 2 ULIRGs are DOGs

• Contribute a ~quarter of the total IR luminosity

density at z~2

• Space density + clustering => ~3-4L* elliptical at z=0

• Bright DOGs ~ Power-Law ~ compact ~ (obscured)

AGN

• Faint DOGs ~ Bump ~ diffuse, interacting ~ SF

• Herschel will help pin down FIR SED, which is a

major existing uncertainty.

Need FIR SEDs to reassess!

What is a DOG?

A ULIRG at z = 2, selected at 24 micron