HEROs in an Overdense Region at z=2.4

HEROs in an Overdense Region at z=2.4

Myungshin Im (Seoul National University)& IRAC GTO team (PI: G. Fazio)

Partial List of Collaborators:M. Pahre, H. Smith, S. Willner (SAO) + IRAC GTO.M. Lacy, F. Marleau, D. Fadda (SSC).

According to the Cambridge International Dictionary of English,

Hero, female also heroine (PERSON) noun[C]

a person who is admired for having done something very brave or having achieved something great, or the main character in a book, film or play, esp., one who is admired for their good qualities.

Hero, submarine sandwich (FOOD), noun[C]

AMERICAN

a long thin sandwich filed with cold meat, cheese, and salad.

HERO, (OBJECT), noun[C]

ASTRONOMY

acronym for “Hyper Extremely Red Objet”. An astronomical object (very possibly a galaxy) which is invisible in the optical, and has a very red near-infrared (NIR) color (J-K > 3, Totani et al. 2001).

?

What is HERO?

August 2005, Lijiang, Extreme Starburst

Actually, a Member of ERO (Extremely Red Object) Family…

• (Normal) ERO: Optical – NIR Color Selected EROs (R-K > 5, I-K > 4 mag) – z > 1

• HERO (Hyper ERO): J-K > ~ 3.0 (Totani et al. 2001; Im et al. 2002) – z > 2.4

• IERO (IR-Selected ERO): IRAC-Color Selected EROs (Yan et al. 2004).

• NERO (NIR-Selected ERO): J-K Red Galaxies – z > 1.5-2.0


HERO (Hyper Extremely Red

Object)

Im et al.(2002)

J-K >~3mag

z=2-3 old galaxy or z=2-3 dusty galaxy or z=10-13 LBG.


Old Galaxy at High Redshift

ERO Study was originally aimed to search for high-z massive, early-types.


Young and Dusty Galaxy (Extreme Starburst?!)

But, people realized that ERO population include many dusty starforming galaxies (~ 50%, e.g., Yan et al. 2004).


Infant Galaxy Shortly After Big Bang


Galaxy Formation in CDM Universe

1. Is is true that there are very few massive, old galaxies at high redshift?

2. When is the formation epoch of massive, old galaxies?

3. Is there any dependence on environment? (early formation in cluster?)

Predictions: Fewer massive early-types at higher redshift. Earlier formation of massive objects in cluster environment.

Need for HEROs

53W002 Field1. 53W002 is a radio galaxy at z=2.4.

2. Lyman-alpha emitters at z ~ 2.4 in the vicinity of 53W002 (Keel et al. 1999; Pascarelle et al. 1996; Windhorst et al. 1997) z=2.4 cluster of galaxies?

3. Recent observations reveal that this field contain other interesting objects, such as submm galaxies (Smail et al. 2002), and dozens of HEROs (Hyper Extremely Red Objects; Im et al. 2002).

Is this a high-z galaxy cluster?When did early-type galaxies form in cluster environment?


Color-Magnitude Relation

Z=1

Z=2Z=3

K

J-K

Im et al. (2005), fromPalomar 5-m WIRC Obs.

20 22

2

3 2.7


53W002 vs. CDF-South

K (Vega)

J-K

53W002

CDF-S

K (Vega)18 vs 2


Redshift Distribution(53W002)

Overdensity at z ~ 2.4 !(Keck LRIS-B: Colbert & Malkan 2005)

Spitzer Observation of the 53W002 Field

1 Hour Exposure in Each Passband (3.6, 4.5, 5.6, 8 micron). Field of View: 5x5 sq. arcmin. Sensitivity: 1 Jy at 3.6 & 4.5 microns, 5 Jy otherwise.

(M. Pahre)

Palomar WIRC Image (K, 2’ by 2’ Zoom-In)

7 hrs on 5-m

Green Circle:53W002_HERO1 with K=21.5 mag

Spitzer IRAC Image (2’ by 2’ Zoom-In)

1 hr on 0.85m

SED of HEROs 1 (Old or Dusty Galaxy at z ~ 2.4

• SED of the HERO is consistent with a moderately old galaxy at z ~ 2.4• Stellar Mass of this object could be 1012 M_sun (Similar to Massive Galaxies at

z=0 (Im et al. 2005, in preparation).

SED of HEROs 2: AGN?

SED of Lyman-alpha Emitters (z ~ 2.4)

53W002 Submm

Starforming

Fnu(uJy)

Wavelength (micron)

Conclusions• HEROs: -Not Lyman-break galaxies at z ~ 12. -Massive Red galaxies at z ~ 2.4 -Old or Dusty? Not Clear Yet. -Age > a few hundred Myrs (dusty). Age > 1Gyr (old) -E-like (3/11), AGN-like (3/11), Intermediate (5/11).• Lyman-alpha emitters: AGN or Young Gs (~ 50 – 10

0 Myr).• Spitzer Cycle 2 observation (MIPS 24) is underway to

determine how dusty these HEROs and Lyman-alpha emitters are.

HEROs in an Overdense Region at z=2.4

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