Transcript Far-Ultraviolet Imaging of the Hubble Deep Field North H. I. Teplitz1, T.M.

Far-Ultraviolet Imaging of the Hubble Deep Field North
H. I. Teplitz1, T.M. Brown2, C. Conselice3, D.F. de Mello4,5,6, M.E. Dickinson2, H.C. Ferguson2, J.P. Gardner3, M. Giavalisco2, F. Menanteau6
(1) Spitzer Science Center, (2) STScI, (3) Caltech, (4) GSFC, (5) CUA, (6) JHU
Motivation
Observations
The ultraviolet imaging capability of MAMA detectors onboard
HST offers a unique opportunity to extend the legacy of the
Hubble Deep Field North (HDF-N; Williams et al. 1996). We
present new ACS-SBC imaging of the HDF in the far-ultraviolet
(1500 Angstroms; FUV), combined with previous STIS FUV
imaging (Gardner, Brown & Ferguson 2000). We:
• detect galaxies 10x fainter than GALEX ultra-deep surveys
• observe high spatial resolution FUV morphologies for galaxies
out to z~0.7
• compute galaxy number-magnitude counts and examine the
effect of moderate redshift starbursts
Redshifts
• Published spectroscopic redshifts are available for 53 of the 111
FUV detected sources (Cohen et al. 2000, 2001; Dawson et al.
2001). One spectrum shows the object to be a star.
• For the remaining objects, high accuracy photometric redshifts
have been estimated based on WFPC2 U300B450V606I814, NICMOS
J110H160, and ground-based Ks (Budavari et al. 2000 in most
cases; Fernadez-Soto 1999 for 6 disputed objects).
• For two objects, the published zphot identify the galaxy at z>1.
However, when we re-estimate the redshift including the FUV
detection, we find a lower value.
• The redshift distribution is shown in figure 4.
•28 CVZ orbits in Cycles 11 to cover 2/3 of the original
WFPC2 HDF-N area
–F150LP filter
–14 pointings, 31”x35” field of view
–10240 seconds per pointing
•1/3 of HDF-N with STIS FUV-MAMA
•Data reduction follows Brown et al. (2000)
•Images drizzled onto WFPC2 HDF-N plate scale and
orientation (Figure 1).
•Detection limits are a strong function of position on the
detector due to dark current glow. In the low dark current
regions, 4s limits magnitudes are
• STIS:AB=30
ACS: AB=29
•Photometry is measured in isophotal apertures determined
by 3.5s in WFPC2 V+I image.
•111 objects detected in FUV
Number Counts
• We measure galaxy number-magnitudes for the ACS sources
and compare them to the published STIS counts (figure 2).
• Dark current variation complicates the measurement of the
counts. We use the procedure outlined in Gardner et al. 2000.
First, we use the variance map to determine the area over which
each galaxy would have been detected. Then, we correct from
isophotal to total magnitude for each galaxy based on simulations
of the object detection procedure in the V+I catalog (Ferguson
1998). The correction is small (<20%) for most sources.
Figure 1: Two color composite image – the white on black background image is the F450W (B-band) WFPC2
mosaic of the HDF-N; the “violet” overlay shows the FUV image on the same pixel scale.
Discussion
• The FUV number counts are surprisingly flat compared to the
predicted counts (Granato et al. 2000).
• A larger population of strongly star-forming galaxies would
increase the number of bright galaxies and decrease the number
of faint ones.
• Further flattening of the counts will occur if the duty cycle for
starbursts is short, followed by a long period of quiescence. Such
a scenario would indicate that the galaxies at the bright end of the
counts are undergoing a single, rapid burst of star-formation and
will later evolve into the UV-faint galaxies.
• Flattening of the counts might also occur if bright end counts
capture galaxies undergoing one of multiple short bursts of starformation. This scenario would imply steeper counts at the faint
end where our statistics are poor.
• GALEX will definitively measure the bright end of the counts.
Figure 4: Redshift distrubtion of FUV detections (top) and redshift vs. absolute
magntidue, MB, for all HDF objects with FUV detections circled (bottom), as a
function of galaxy morphology.
FUV150 NUV300
I814
H160
FUV150 NUV300
I814
H160
0.090
0.199
0.321
0.321
Morphology
0.321
0.321
• As expected, most FUV detections are of late type systems. The
FUV images highlight the regions of strong star-formation and low
dust content.
• Some galaxies show strong evidence of the “morphological Kcorrection” (Bohlin et al. 1991; Papovich et al. 2003). See Fig 3.
• Each galaxy was classified by eye in the F814W image.
• We detect 1/3 of ellipticals at z<1 in the HDF
0.475
0.485
0.555
0.561
0.682
0.753
– Most of these are the lower mass (M*<1010) and less luminous (MB > -20)
E’s in the field
Blue Core Ellipticals
•Menanteau et al. (2001) identify resolved blue cores in HDF-N
ellipticals, suggesting a population of spheroids that that have
undergone recent merger or residual star formation activity.
Figure 5: Redshift vs. blue core. Delta(V-I) indicates the intensity the blue core.
Red symbols indicate FUV-detected objects
Figure 2: Galaxy number-magnitude counts compared to predictions from the model of Granato et al.
(2000). Magnitudes have been corrected from isophotal to total.
•The ellipticals with the bluest cores are detected in the FUV (see
Fig. 5)
Figure 3: The Morphological K-correction. Spectroscopic redshifts are indicated.
Bohlin, R.C., et al. 1991, ApJ, 368, 12
Brown, T.M., et al. 2000, AJ, 120, 1153
Budavari, T., Szalay, A.S., Connolly, A.J.,
Csabai, I., & Dickinson, M. 2000, AJ, 120, 1588
Cohen, J.G., et al. 2000, ApJL, 471, 5
Cohen, J.G. 2001, AJ, 121, 2895
Dawson, S., Stern, D., Bunker, A.J., Spinrad, H., &
Dey, A. 2001, AJ, 122, 598
Dickinson, M., et al. 2000, ApJ, 531, 624
Ferguson, H.C. 1998, in “The Hubble Deep Field”,
ed. Livio, Fall & Madau, 181
Fernadez-Soto, et al. 1999, ApJ, 513, 34
Gardner, J.P. Brown, T.M., & Ferguson, H.C. 2000, ApJL, 542, 79
Granato, G.L. et al., 2000, ApJ, 542, 710
Menanteau, F., Jimenez, R., & Matteucci, F. 2001, ApJL, 562, 23
Papovich, C., et al. 2003, ApJ, 598, 827
Williams, R.E. et al. 1996, AJ, 11, 1335
We thank Robert Hurt for preparing the two color composite image. We thank James Colbert for help with the new photometric redshifts. The research described
in this poster was carried out, in part, by the Jet Propulsion Laboratory, California Institute of Technology, and was sponsored by National Aeronautics and Space
Administration.
Cycle 13
A Treasury program has been approved
for Cycle 13 to obtain Ultraviolet imaging
of the Ultra-Deep Field (GO-10403).
Subject to scheduling constrants, the
program includes:
•50 orbits of FUV
•12 orbits of F300W
•Parallel imaging w/ NICMOS