HEROs in an Overdense Region at z=2.4

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HEROs in an Overdense Region at z2.4
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).
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What is HERO?
According to the Cambridge International
Dictionary of English,
Hero, female also heroine (PERSON) nounC 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),
nounC AMERICAN a long thin sandwich filed
with cold meat, cheese, and salad.
HERO, (OBJECT), nounC 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 gt 3, Totani et al.
2001).
?
August 2005, Lijiang, Extreme Starburst
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Actually, a Member of ERO (Extremely Red Object)
Family

• (Normal) ERO Optical NIR Color Selected EROs
  (R-K gt 5, I-K gt 4 mag) z gt 1
• HERO (Hyper ERO) J-K gt 3.0 (Totani et al.
  2001 Im et al. 2002) z gt 2.4
• IERO (IR-Selected ERO) IRAC-Color Selected EROs
  (Yan et al. 2004).
• NERO (NIR-Selected ERO) J-K Red Galaxies z gt
  1.5-2.0

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HERO (Hyper Extremely Red Object)
J-K gt3mag z2-3 old galaxy or z2-3 dusty
galaxy or z10-13 LBG.
Im et al. (2002)
August 2005, Lijiang, Extreme Starburst
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Old Galaxy at High Redshift
ERO Study was originally aimed to search for
high-z massive, early-types.
August 2005, Lijiang, Extreme Starburst
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Young and Dusty Galaxy (Extreme Starburst?!)
But, people realized that ERO population include
many dusty starforming galaxies ( 50, e.g.,
Yan et al. 2004).
August 2005, Lijiang, Extreme Starburst
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Infant Galaxy Shortly After Big Bang
August 2005, Lijiang, Extreme Starburst
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Galaxy Formation in CDM Universe

• 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
August 2005, Lijiang, Extreme Starburst
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53W002 Field

• 53W002 is a radio galaxy at z2.4.
• Lyman-alpha emitters at z 2.4 in the vicinity
  of
• 53W002 (Keel et al. 1999 Pascarelle et al.
  1996
• Windhorst et al. 1997) ? z2.4 cluster of
  galaxies?
• 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?
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Color-Magnitude Relation
Im et al. (2005), from Palomar 5-m WIRC Obs.
Z3
Z2
3
2.7
2
J-K
Z1
20
22
K
August 2005, Lijiang, Extreme Starburst
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53W002 vs. CDF-South
53W002
CDF-S
J-K
K (Vega)
K (Vega)
18 vs 2
August 2005, Lijiang, Extreme Starburst
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Redshift Distribution(53W002)
Overdensity at z 2.4 ! (Keck LRIS-B Colbert
Malkan 2005)
August 2005, Lijiang, Extreme Starburst
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Spitzer Observation of the 53W002 Field
(M. Pahre)
1 Hour Exposure in Each Passband (3.6, 4.5, 5.6,
8 micron). Field of View 5x5 sq. arcmin.
Sensitivity 1 m Jy at 3.6 4.5 microns, 5 m Jy
otherwise.
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Palomar WIRC Image (K, 2 by 2 Zoom-In)
7 hrs on 5-m
Green Circle 53W002_HERO1 with K21.5 mag
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Spitzer IRAC Image (2 by 2 Zoom-In)
1 hr on 0.85m
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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 z0 (Im et al.
  2005, in preparation).

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SED of HEROs 2 AGN?
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SED of Lyman-alpha Emitters (z 2.4)
Submm
53W002
Fnu (uJy)
Starforming
Wavelength (micron)
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Conclusions

• HEROs
• -Not Lyman-break galaxies at z 12.
• -Massive Red galaxies at z 2.4
• -Old or Dusty? Not Clear Yet.
• -Age gt a few hundred Myrs (dusty). Age gt
  1Gyr (old)
• -E-like (3/11), AGN-like (3/11),
  Intermediate (5/11).
• Lyman-alpha emitters AGN or Young Gs ( 50
  100 Myr).
• Spitzer Cycle 2 observation (MIPS 24) is underway
  to determine how dusty these HEROs and
  Lyman-alpha emitters are.