Extremely Red Galaxies with RJ5: Testing Galaxy Evolution

1
Extremely Red Galaxies with R-J5 Testing
Galaxy Evolution
Angela Hempel1, Tom Herbst2, Dave Thompson3

• Observatory Geneva
• Max-Planck Institute Heidelberg
• Caltech

2
Outline

• Why and How?
• The reason behind the color limit
• R-J 5
• Data
• Results
• J-band number counts
• color distribution
• surface / volume density
• Multi-color follow-up
• Summary outlook

Longhetti et al., 2005, astro-ph/0505467
3
Why and How ?

• surveys like GDDS, GOODS K20 find numerous
  massive evolved galaxies at high redshifts,
• question not only when did the stellar mass
  assemble, but also by which process, quiescent
  star formation, or starburst does the assembly
  occur?
• 1/3 of stellar mass in place at z1.8 (Glazebrook
  et al. 2004)
• Solution star formation must have been very
  intense in the progenitors of these systems
  (similarities to monolithic collapse.)

Glazebrook et al., 2004
4
Extremely Red Colors

• Optical near-infrared
• R-K5, 5.3, 6, 7
• I-K4
• R-J5 ?
• NIR NIR J-K3,4 HEROs (difficult to explain
  by old populations

• ellipticals
• starburst
• (simple) spirals

1lt z lt 2
Yan Thompson 2003
Im et al., 2002
Moustakas et al., 2004
5
Whats so special on R-J5?

• Practical reasons
• bright near-infrared magnitudes allow for
  spectral follow up,
• as well as indicating the galaxy being a massive
  object,
• possibilities for interpretations
• R-K vs. J-K leaves room for false interpretations
  
• not because of increasing extinction but because
  of non-detections in 1 or 2 bands.

Pozzetti Mannucci 2000
Good guess R-J 5 dominated by old populations
in elliptical galaxies.
Berström Wiklind 2004
6
Color Redshift evolution

• elliptical galaxies
• starbursts
• spiral galaxies
• formation redshift
• star formation rate
• initial mass function
• metallicity
• extinction (spirals and star bursts)
• orientation (spiral galaxies)
• When, how and why become galaxies
• extremely red?

7
Elliptical Galaxies I

• Instantaneous burst
• SFR?(t)
• sepearates effect of aging and increasing
  metallicity of the ISM
• for Zlt0.2 Z? not even the highest formation
  redshift yields red enough colors,
• R-J ? 5 needs solar metallicity and zfgt3

8
Elliptical Galaxies II

• continued star formation
• SFR exp(-t/?)
• i.e. hot merger
• or long ? ( with lower SFR)
• UV/ blue radiation of new hot stars counteracts
  aging
• later aging dominates later,
• increasing higher initial metallicity of new
  stars, i.e. their color is slightely redder even
  if their stellar population is in average
  slightely redder than after a burst.

• zmin 3, ?max 100 Myr for EROs

9
Starburst

• EROs sample based on R-Kgt5..6 selection contains
  a substantial fraction of starburst galaxies.
• How about R-J5?
• SFR 510-5M?Myr-1 per solar mass (25 M? per year
  for a 51011 M?)
• constant star formation for 100 Myr
• variable E(B-V) 1, 2, 3
• extinction laws by Calzetti et al 2000

Even for E(B-V)3.0, starbursts do not enter the
ERO region before z4!
10
Spiral Galaxies

• detections of F814 -Ks4 objects
• high fraction of disk structures (edge-on)
• SFR constant or exp(-t/?)
• edge on or averaged orientation
• not including passive spirals

Our sample of EROs contains no spiral galaxies!
11
Possible EROs Candidates?
zlt2.1
zlt3

• The classification of R-J5 EROs as elliptical
• galaxies with an old stellar population (zfgt3)
• does not imply their formation due to a
• monolithic collapse, but simply constrains
• the epoch of formation.

1ltzlt2
Photometric separation works well for R-J 5 !
12
Data

• optical High-Z Supernova Search Project
  (photometric calibration with SDSS) Rlimit
  lt24-25mag
• near-infrared (J-band) OMEGA Prime (Calar Alto),
  J15-20.5mag
• in total 79 fields (4.64 deg2), arranged in
  groups or single

13
J-band Number Counts

• 2 slopes
• 12.50ltJlt17.25 ? 0.54 ? 0.01
• 17.25ltJlt19.00 ? 0.33 ? 0.04
• Compared to surveys with only one or a few
  contiguous fields, the large number of disjoint
  fields largely eliminates large scale structure
  as a source of uncertainty.

14
Color-Magnitude Distribution

• increase in mean color by 1.55 magnitudes
• result of growing fraction of high redshift
  galaxies
• (The second subsidiary peak at faint magnitudes
  is solely the result of using the limiting R-band
  magnitudes for optical non-detection.)

15
EROs with R-J5

• Galaxies with R-detection 88
• Galaxies without R-detection 47
• Objects fainter than J 18.75 24
• ? (0.970.07) x 10-2 arcmin-2 and J19.5 mag
• (J-K 2.3 from stellar population models)
• Daddi et al., 2000, R-K?7,
• ? 0.011 arcmin-2, based on 5 objects

10-2
10-3
10-4
16
Spatial distribution

• inhomogeneous spatial distribution (but not fit
  to determine 2d-correlation function)
• at z2, an ISAAC field corresponds to 1.27 Mpc,
  the core size of a cluster,
• 2 confirmed EROs in a 2.5 arcmin field 3 times
  higher surface density than EROs in the field,

?
17
Volume density

• Redshift estimate
• 1.4 z 2, 3
• Volume density
• z2 (10.1 0.8) 10-5 h703Mpc-3
• z3 ( 4.7 0.4) 10-5 h703Mpc-3
• Does ?CDM form enough massive DM halos to harbor
  the observed number of massive galaxies at a
  given redshift?
• YES, if EROs live in halos of 1013.3M?

K20
18
Multi-color follow-up
R-J6.47 J-K0.87

• 6 pre-selected fields (27.1 arcmin2)
• 15 R-K5 EROs, ? (0.550.14) arcmin-2
• 1 ERO with R-J5, ? 0.0369 arcmin-2
• from survey (0.970.07) 10-2armin-2
• expect no object in this area!
• but found one!

19
Pozzetti Mannucci 2000

• exceptional red object with R-J6.47 and
  R-K7.44, J-K0.87
• J-K color of stellar object (morphology!)
• dominant fraction of evolved ellipticals
  (Moriondo et al. 2000, Cimatti et al. 1999)

20
Morphology

• the single re-identified ERO (i) has no optical
  detection (7sigma)

multiple sources (e,f), two of them are EROs
21
Summary

• R-J5 preferentially selects evolved galaxies,
  where the stellar mass component has been formed
  at zgt3.
• massive structures have formed early
• but EROs are clustered, and galaxy formation is
  accelerated in dense environments
• (massive field ellipticals appear several Gyrs
  younger than cluster ellipticals)
• Co-moving volume density
  (4.710.37) 10-5 h703 Mpc-3 (zup 3)
• Next step more multi-color observations,
  photometric redshift estimates and spectroscopy
  to support our classification as evolved stellar
  population!