Galaxies under the cosmic microscope: Resolved spectroscopy and new constraints on the z = 1 Tully-Fisher relation
Monthly Notices of the Royal Astronomical Society 368:4 (2006) 1631-1645
Abstract:
We exploit the gravitational potential of massive cluster lenses to probe the emission-line properties of six galaxies which appear as highly magnified luminous arcs. Using the Gemini Multi-Object Spectrograph (GMOS) integral field spectrograph together with detailed cluster lens models, we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to ∼0.5 kpc (unlensed) at . Four of the galaxies have stable disc-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I-band Tully-Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B band, the observations suggest of brightening, consistent with increased star-formation activity at . However, the galaxies with stable disc kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counterparts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high-redshift Universe than that possible with conventional surveys. © 2006 RAS.Star forming galaxies at z ≈ 6 and reionization
New Astronomy Reviews 50:1-3 SPEC. ISS. (2006) 94-100
Abstract:
We determine the abundance of i′-band drop-outs in the HST/ACS GOODS surveys and the Hubble Ultra Deep Field (UDF). The majority of these sources are likely to be z ≈ 6 galaxies whose flux decrement between the F775W i′-band and F850LP z′-band arises from Lyman-α absorption. We have shown with Keck/DEIMOS and Gemini/GMOS spectroscopy that this technique does indeed select high redshift galaxies, and we discovered Lyman-α emission in the expected redshift range for about a third of the galaxies with z′AB < 25.6 in the 150 arcmin2 of the GOODS-South field. The i-drop number counts in the GOODS-North field are consistent, so cosmic variance is possibly not be the dominant uncertainty. The increased depth of UDF enables us to reach a ∼10σ limiting magnitude of z′AB = 28.5 (equivalent to 1.5 h70-2 M⊙ yr-1 at z = 6.1, or 0.1 LUV* for the z ≈ 3 U-drop population). The star formation rate at z ≈ 6 was approximately ×6 less than at z ≈ 3. This declining comoving star formation rate (0.005 h70 M⊙ yr-1 Mpc-3 at z ≈ 6 at LUV > 0.1L* for a Salpeter IMF) poses an interesting challenge for models which suggest that LUV > 0.1L* star forming galaxies at z ≃ 6 reionized the universe. The short-fall in ionizing photons might be alleviated by galaxies fainter than our limit, or a radically different IMF. Alternatively, the bulk of reionization might have occurred at z ≫ 6. We have recently discovered evidence of an early epoch of star formation in some of the i′-drops at z ≈ 6. Spitzer images with IRAC at 3.6-4.5 μm show evidence of the age-sensitive Balmer/4000 Å, dominated by stars older than 100 Myr (and most probably 400 Myr old). This pushes the formation epoch for these galaxies to zform = 7.5-13.5. There are at least some galaxies already assembled with stellar masses ≈3 × 1010 M⊙ (equivalent to 0.2 M* today) within the first billion years. The early formation of such systems may have played a key role in reionizing the Universe at z ∼ 10. © 2005 Elsevier B.V. All rights reserved.The star formation rate at redshift one: Ha spectroscopy with CIRPASS
Monthly Notices of the Royal Astronomical Society 370:1 (2006) 331-342
Abstract:
We have conducted an Hα survey of 38 0.77 < z < 1 galaxies over ∼100arcmin2 of the Hubble Deep Field-North and Flanking Fields, to determine star formation rates (SFRs), with the near-IR multi-object spectrograph Cambridge Infrared Panoramic Survey Spectrograph (CIRPASS) on the William Herschel Telescope (WHT). This represents the first successful application of this technique to observing high-redshift galaxies. Stacking the spectra in the rest frame to infer a total SFR for the field, we find a lower limit (uncorrected for dust reddening) on the SFR density at redshift z = 1 of 0.04 M⊙ yr-1 Mpc-3. This implies rapid evolution in the SFR density from z = 0 to 1 which is proportional to (1+ z)3.1 © 2006 RAS.The las campanas infrared survey - V. Keck spectroscopy of a large sample of extremely red objects
Monthly Notices of the Royal Astronomical Society 361:2 (2005) 525-549
Abstract:
We present deep Keck spectroscopy, using the Deep Imaging Multi-Object Spectrograph and the Low-Resolution Imaging Spectrometer spectrographs, of a large and representative sample of 67 extremely red objects (EROs) to H = 20.5 in three fields (SSA22, Chandra Deep Field South and NTT Deep Field) drawn from the Las Campanas Infrared Survey (LCIRS). Using the colour cut (I - H) > 3.0 (Vega magnitudes) adopted in earlier papers in this series, we verify the efficiency of this selection for locating and studying distant old sources. Spectroscopic redshifts are determined for 44 sources, of which only two are contaminating low-mass stars. When allowance is made for incompleteness, the spectroscopic redshift distribution closely matches that predicted earlier on the basis of photometric data. Our spectra are of sufficient quality that we can address the important question of the nature and homogeneity of the z > 0.8 ERO population. A dominant old stellar population is inferred for 75 per cent of our spectroscopic sample, a higher fraction than that seen in smaller, less complete samples with broader photometric selection criteria (e.g. R - K). However, only 28 per cent have spectra with no evidence of recent star formation activity, such as would be expected for a strictly passively evolving population. More than ∼30 per cent of our absorption-line spectra are of the 'E+A' type with prominent Balmer absorption consistent, on average, with mass growth of 5-15 per cent in the past gigayear. We use our spectroscopic redshifts to improve earlier estimates of the spatial clustering of this population as well as to understand the significant field-to-field variation. Our spectroscopy enables us to pinpoint a filamentary structure at z = 1.22 in the Chandra Deep Field South. Overall, our study suggests that the bulk of the ERO population is an established population of clustered massive galaxies undergoing intermittent activity consistent with continued growth over the redshift interval 0.8 < z < 1.6. © 2005 RAS.Near-infrared properties of i-drop galaxies in the Hubble ultra deep field
Monthly Notices of the Royal Astronomical Society 359:3 (2005) 1184-1192