Volume 538, February 2012
|Number of page(s)||13|
|Published online||30 January 2012|
The evolving slope of the stellar mass function at 0.6 ≤ z < 4.5 from deep WFC3 data
1 INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
2 Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA
3 INAF - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
Received: 17 June 2011
Accepted: 24 November 2011
We used Early Release Science (ERS) observations taken with the Wide Field Camera 3 (WFC3) in the GOODS-S field to study the galaxy stellar mass function (GSMF) at 0.6 ≤ z < 4.5. Deep WFC3 near-IR data (for Y as faint as 27.3, J and H as faint as 27.4 AB mag at 5σ), as well as deep KS (as faint as 25.5 at 5σ) Hawk-I band data, provide an exquisite data set with which determine in an unprecedented way the low-mass end of the GSMF, allowing an accurate probe of masses as low as M∗ ≃ 7.6 × 109 M⊙ at z ~ 3. Although the area used is relatively small (~33 arcmin2), we found generally good agreement with previous studies on the entire mass range. Our results show that the slope of the faint-end increases with redshift, from α = −1.44 ± 0.03 at z ~ 0.8 to α = −1.86 ± 0.16 at z ~ 3, although indications exist that it does not steepen further between z ~ 3 and z ~ 4. This result is insensitive to any uncertainty in the M∗ parameter. The steepness of the GSMF faint-end solves the well-known disagreement between the stellar mass density (SMD) and the integrated star-formation history at z > 2. However, we confirm that there appears to be an excess of integrated star formation with respect to the SMD at z < 2, by a factor of ~2−3. Our comparison of the observations with theoretical predictions shows that the models forecast a greater abundance of low mass galaxies, at least up to z ~ 3, as well as a dearth of massive galaxies at z ~ 4 with respect to the data, and that the predicted SMD is generally overestimated at z ≲ 2.
Key words: galaxies: luminosity function, mass function / galaxies: evolution / galaxies: high-redshift / galaxies: fundamental parameters
© ESO, 2012
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