Download Evolution of the Mass-to-light Ratio of Galaxies to z~0.25

Evolution of the Mass-to-light Ratio of Galaxies to z~0.25
Barbara Catinella1, Martha P. Haynes2, Jeffrey P. Gardner3, Andrew J. Connolly3, & Riccardo Giovanelli2
1
Arecibo Observatory,
2
Cornell University, 3Pittsburgh University
Introduction
Sample Selection and Arecibo Observations
A very interesting and much debated issue is the evolution of the Tully-Fisher
relation (TFR) over cosmic time. If galaxies were more luminous in the past, we
should observe an offset in the TFR derived independently at high and low
redshift z (i.e., a change of its zero point). However, studies based on optical
spectroscopy (see, e.g., [1] and references therein) have reached conflicting
conclusions. Results vary from substantial luminosity evolution (in excess of one
magnitude with respect to the z=0 TFR) even at modest z to no significant change
up to z~1. Evidence for evolution of the TFR or its lack remains inconclusive.
The targets for HI spectroscopy were extracted from the Sloan Digital Sky Survey
(SDSS) database based on their z, optical emission line strength, inclination, disk
morphology, and relative isolation. The observations were carried with the 305m
Arecibo radiotelescope in standard position-switching mode.
We have undertaken a targeted survey with the 305m Arecibo radiotelescope to
detect HI-line emission from disk galaxies at z>0.16. Compared to optical widths,
HI measurements sample a larger fraction of the disks, where the rotation curves
are typically flat, and are not affected by slit smearing and misalignment or by
aperture effects. Thus, in contrast to studies based on optical spectroscopy, this
data set allows us to perform a direct comparison with the local TFR that is
technique independent.
Detection of 21 cm emission from galaxies at z>0.1 is difficult, due to the
weakness of the signals, radio frequency interference (RFI), and increased beam
confusion. Accurate z must be known in advance. This project has become
feasible only recently, thanks to technical improvements at Arecibo (most
importantly the installation of the new L-wide receiver, which gives access to
frequencies down to 1.12 GHz, in Feb 2003) and to the availability of the SDSS.
Of 33 galaxies targeted with adequate integration time, 26 were detected. Here
we present 12 of 20 usable HI profiles that have been fully processed. The
redshift of these objects is 0.17≤z≤025; the average on-source integration time
ranged between 1 and 3 hours.
The Highest Redshift Detections of HI Emission From Normal Galaxies Ever Made!!!
z = 0.1682
Ton = 52 m
SDSS J020849.45+130442.5
z = 0.1879
Ton = 80 m
SDSS J120948.14+100822.5
z = 0.2031
Ton = 88 m
SDSS J134211.36+053211.5
AGC 122040
AGC 224321
z = 0.2239
Ton = 184 m
SDSS J111645.15+054210
AGC 232055
AGC 212941
10"
z = 0.1712
Ton = 84 m
SDSS J082522.13+325953.6
z = 0.1909
Ton = 148 m
SDSS J003610.7+142246.4
z = 0.2067
Ton = 136 m
SDSS J110730.34+072350.2
AGC 181518
AGC 101750
AGC 212966
z = 0.2455 !!!
Ton = 176 m
SDSS J142735.69+033434.2
AGC 242147
z = 0.1754
Ton = 80 m
SDSS J151337.28+041921.1
z = 0.1954
Ton = 156 m
z = 0.1763
z = 0.2189
Ton = 132 m
SDSS J160938+312958.5
SDSS J140522.72+052814.6
AGC 252580
AGC 242091
AGC 262029
Ton = 96 m
SDSS J091957+013851.6
AGC 191728
SDSS images and calibrated, smoothed HI spectra of the 12 fully reduced detections. The size of each SDSS image is 1.5' (the size
of the Arecibo beam at 1.2 GHz is ~4'). The red line in each spectrum indicates the frequency corresponding to z from the SDSS.
The panel under each spectrum shows the percentage of data that was used at each frequency, after RFI excision and rejection of
bad records. The object in the red box represents the highest z detection of HI emission from a normal galaxy to date (the previous
published record belongs to a galaxy at z=0.1766 in Abell 2218, [3]). Velocity widths W50 were measured at the 50% level of the HI
profiles, corrected and deprojected to edge-on view. The HI mass range for this sample is 2-6 1010 M‫ּס‬.
Tully-Fisher Relation Evolution?
Conclusions
Thanks to upgrades at the Arecibo Observatory and the availability of the SDSS
database, detection of HI emission from galaxies at z>0.1 has recently become
feasible. However, such observations are still very challenging, due to the
weakness of the signals, presence of RFI, and increased beam confusion.
We obtained HI profiles of adequate quality for velocity width measurements for
20 galaxies with 0.17 ≤ z ≤ 0.25, 12 of which have been fully processed. Total
average integration times (half spent on-source) ranged between 2 and 6 hours,
making these observations for a significant number of objects currently feasible
only at Arecibo.
Preliminary look at the TF diagram for the 12 galaxies shown above (H0=70 km/s
Mpc-1). Red (blue) symbols indicate objects with z>0.20 (z<0.20). The solid and
dotted lines represent the I-band TFR and its scatter, as derived by [2].
This preliminary result does not suggest evidence for a systematic increase of
galaxy luminosity at z~0.2 compared to the local TFR. However, an accurate
evaluation of the uncertainties and the selection biases of this sample is
necessary before a conclusion can be drawn.
A preliminary look at the TF diagram for these detections does not suggest
evidence of evolution of the TF zero point. However, an accurate understanding
of the uncertainties and selection biases of this sample is necessary before a
conclusion can be reached.
REFERENCES:
[1] Flores, H. et al. 2006, A&A, 455, 107
[2] Giovanelli, R. et al. 1997, AJ, 113, 53
[3] Zwaan, M. A. et al. 2001, Science, 293, 1800