Ignacio Trujillo

The size evolution of galaxies since z~3: combining SDSS, GEMS, and FIRES

We present the evolution of the luminosity-size and stellar mass-size relations of luminous ( L-V greater than or similar to 3.4 x 10(10) h(70)(-2) L-circle dot) and massive ( M-* greater than or similar to 3 x 10(10) h(70)(-2) M-circle dot) galaxies in the last similar to 11 Gyr. We use very deep near-infrared images of the Hubble Deep Field-South and the MS 1054-03 field in the J(s), H, and K-s bands from FIRES to retrieve the sizes in the optical rest frame for galaxies with z > 1. We combine our results with those from GEMS at 0.2 < z < 1 and SDSS at z similar to 0.1 to achieve a comprehensive picture of the optical rest-frame size evolution from z = 0 to 3. Galaxies are differentiated according to their light concentration using the Sersic index n. For less concentrated objects, the galaxies at a given luminosity were typically similar to 3 +/- 0.5 ( +/- 2 sigma) times smaller at z similar to 2: 5 than those we see today. The stellar mass-size relation has evolved less: the mean size at a given stellar mass was similar to 2 +/- 0.5 times smaller at z similar to 2.5, evolving proportionally to ( 1 + z) - 0.40 +/- 0.06. Simple scaling relations between dark matter halos and baryons in a hierarchical cosmogony predict a stronger ( although consistent within the error bars) than observed evolution of the stellar mass-size relation. The observed luminosity-size evolution out to z similar to 2.5 matches well recent infall model predictions for Milky Way-type objects. For low-n galaxies, the evolution of the stellar mass-size relation would follow naturally if the individual galaxies grow inside out. For highly concentrated objects, the situation is as follows: at a given luminosity, these galaxies were similar to 2.7 +/- 1.1 times smaller at z similar to 2.5 ( or, put differently, were typically similar to 2.2 +/- 0.7 mag brighter at a given size than they are today), and at a given stellar mass the size has evolved proportionally to ( 1 + z)(-0.45 +/- 0.10).

Strong size evolution of the most massive galaxies since z∼ 2

Using the combined capabilities of the large near-infrared Palomar/DEEP-2 survey, and the superb resolution of the Advanced Camera for Surveys HST camera, we explore the size evolution of 831 very massive galaxies (M_⋆ ≥ 10^(11)h^(−2)_(70) M_⊙) since z ~ 2. We split our sample according to their light concentration using the Sersic index n. At a given stellar mass, both low (n 2.5) concentrated objects were much smaller in the past than their local massive counterparts. This evolution is particularly strong for the highly concentrated (spheroid like) objects. At z ~ 1.5, massive spheroid-like objects were a factor of 4 (±0.4) smaller (i.e. almost two orders of magnitudes denser) than those we see today. These small sized, high-mass galaxies do not exist in the nearby Universe, suggesting that this population merged with other galaxies over several billion years to form the largest galaxies we see today.

Size Evolution of the Most Massive Galaxies at 1.7 < z < 3 from GOODS NICMOS Survey Imaging

We measure the sizes of 82 massive (M ≥ 1011 M☉) galaxies at 1.7 ≤ z ≤ 3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample is almost an order of magnitude larger than previous studies at these redshifts, providing the first statistical study of massive galaxy sizes at z > 2, confirming the extreme compactness of these systems. We split our sample into disk-like (n ≤ 2) and spheroid-like (n > 2) galaxies based on their Sersic indices, and find that at a given stellar mass disk-like galaxies at z ~ 2.3 are a factor of 2.6 ± 0.3 smaller than present-day equal-mass systems, and spheroid-like galaxies at the same redshifts are 4.3 ± 0.7 smaller than comparatively massive elliptical galaxies today. At z > 2 our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (~2 × 1010 M☉ kpc−3) of massive galaxies at these redshifts, which are similar to present-day globular clusters, possibly makes any further evolution in sizes beyond z = 3 unlikely.

THE REST-FRAME OPTICAL LUMINOSITY DENSITY, COLOR, AND STELLAR MASS DENSITY OF THE UNIVERSE FROM z = 0 TO z = 3

We present the evolution of the rest-frame optical luminosity density j, the integrated rest-frame optical color, and the stellar mass density, ?*, for a sample of Ks band-selected galaxies in the Hubble Deep Field-South (HDF-S). We derived j in the rest-frame U, B, and V bands and found that j increases by a factor of 1.9 ? 0.4, 2.9 ? 0.6, and 4.9 ? 1.0 in the V, B, and U rest-frame bands, respectively, between redshifts of 0.1 and 3.2. We derived the luminosity-weighted mean cosmic (U-B)rest and (B-V)rest colors as a function of redshift. The colors bluen almost monotonically with increasing redshift; at z = 0.1, the (U-B)rest and (B-V)rest colors are 0.16 and 0.75, respectively, while at z = 2.8 they are -0.39 and 0.29, respectively. We derived the luminosity-weighted mean M/L, using the correlation between (U-V)rest and log M/L that exists for a range in smooth star formation histories (SFHs) and moderate extinctions. We have shown that the mean of individual M/L estimates can overpredict the true value by ~70%, while our method overpredicts the true value by only ~35%. We find that the universe at z ~ 3 had ~10 times lower stellar mass density than it does today in galaxies with L > 1.4 ? 1010 h L?. Half of the stellar mass of the universe was formed by z ~ 1-1.5. The rate of increase in ?* with decreasing redshift is similar to but above that for independent estimates from the HDF-N, but it is slightly less than that predicted by the integral of the SFR(z) curve.

A correlation between galaxy light concentration and supermassive black hole mass

We present evidence for a strong correlation between the concentration of bulges and the mass of their central supermassive black hole (Mbh)—more concentrated bulges have more massive black holes. Using C(1/3) from Trujillo, Graham, & Caon as a measure of bulge concentration, we find that log(Mbh/M☉) = 6.81(±0.95)C(1/3) + 5.03 ± 0.41. This correlation is shown to be marginally stronger (Spearmans rs = 0.91) than the relationship between the logarithm of the stellar velocity dispersion and log Mbh (Spearmans rs = 0.86) and has comparable or less scatter (0.31 dex in log Mbh, which decreases to 0.19 dex when we use only those galaxies whose supermassive black hole radii of influence are resolved and we remove one well-understood outlying data point).

Stellar Tidal Streams In Spiral Galaxies Of The Local Volume: A Pilot Survey With Modest Aperture Telescopes

Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape all large galaxies to the present day. As a consequence, most seemingly normal disk galaxies should be surrounded by spatially extended stellar “tidal features” of low surface brightness. As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of eight isolated spiral galaxies in the Local Volume, with data taken at small (D = 0.1–0.5 m) robotic telescopes that provide exquisite surface brightness sensitivity (μlim(V ) ∼ 28.5 mag arcsec −2 ). This initial observational effort has led to the discovery of six previously undetected extensive (to ∼30 kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites. In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams. Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks. Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption. A qualitative comparison with available simulations set in a ΛCold Dark Matter cosmology (that model the stellar halo as the result of satellite disruption evolution) shows that the extraordinary variety of stellar morphologies detected in this pilot survey matches that seen in those simulations. The common existence of these tidal features around “normal” disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume.

Extremely compact massive galaxies at z ∼ 1.4

The optical rest-frame sizes of 10 of the most massive (∼5 × 10 11 h −2 M� ) galaxies found in the near-infrared MUNICS survey at 1.2 < z < 1.7 are analysed. Sizes are estimated in both the J and Kfilters. These massive galaxies are at least a factor of 4 +1.9 (±1σ ) smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than that of massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at z ∼ 1.4 (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies.

IRAC Mid-Infrared Imaging of the Hubble Deep Field-South: Star Formation Histories and Stellar Masses of Red Galaxies at z > 2

We present deep 3.6–8 mm imaging of the Hubble Deep Field–South with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We study distant red galaxies (DRGs) at z 1 2 selected by JsKs 1 2.3 and compare them with a sample of Lyman break galaxies (LBGs) at z p 2–3. The observed UV–to–8 mm spectral energy distributions are fitted with stellar population models to constrain star formation histories and derive stellar masses. We find that 70% of the DRGs are best described by dust-reddened star-forming models and 30% are very well fitted with old and “dead” models. Using only the IKs and Ks4.5 mm colors, we can effectively separate the two groups. The dead systems are among the most massive at z ∼ 2.5 (mean stellar mass AM * S p 0.8 #10 11 M,) and likely formed most of their stellar mass at z 1 5. To a limit of 0.5 #10 11 M,, their number density is ∼10 times lower than that of local early-type galaxies. Furthermore, we use the IRAC photometry to derive rest-frame near-infrared J, H, and K fluxes. The DRGs and LBGs together show a large variation (a factor of 6) in the rest-frame K-band mass-to-light ratios (M/LK), implying that even a Spitzer 8 mm–selected sample would be very different from a mass-selected sample. The average M/LK of the DRGs is about 3 times higher than that of the LBGs, and DRGs dominate the high-mass end. The M/LK values and ages of the two samples appear to correlate with derived stellar mass, with the most massive galaxies being the oldest and having the highest mass-to-light ratios, similar to what is found in the low-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift — infrared: galaxies

NICMOS Imaging of DRGs in the HDF-S: A Relation between Star Formation and Size at z ~ 2.5

We present deep, high angular-resolution HST NICMOS imaging in the Hubble Deep Field South (HDF-S), focusing on a subset of 14 distant red galaxies (DRGs) at z ~ 2.5 that have been preselected to have J - K > 2.3. We find a clear trend between the rest-frame optical sizes of these sources and their luminosity-weighted stellar ages as inferred from their broadband spectral energy distributions (SEDs). Galaxies whose SEDs are consistent with being dusty and actively star-forming generally show extended morphologies in the NICMOS images (re 2 kpc), while the five sources that are not vigorously forming stars are extremely compact (re 1 kpc). This trend suggests a direct link between the mean ages of the stars and the size and density of the galaxies and supports the conjecture that early events quench star formation and leave compact remnants. Furthermore, the compact galaxies have stellar surface mass densities that exceed those of local galaxies by more than an order of magnitude. The existence of such massive dense galaxies presents a problem for models of early-type galaxy formation and evolution. Larger samples of DRGs and higher spatial resolution imaging will allow us to determine the universality of the results presented here for a small sample.

A New Empirical Model for the Structural Analysis of Early-Type Galaxies, and A Critical Review of the Nuker Model*

The Nuker law was designed to match the inner few (~3–10) arcseconds of predominantly nearby (30 Mpc) early-type galaxy light profiles; it was never intended to describe an entire profile. The Sersic model, on the other hand, was developed to fit the entire profile; however, because of the presence of partially depleted galaxy cores, the Sersic model cannot always describe the very inner region. We have therefore developed a new empirical model consisting of an inner power law, a transition region, and an outer Sersic model to connect the inner and outer structure of elliptical galaxies. We have additionally explored the stability of the Nuker model parameters. Surprisingly, none are found to be stable quantities; all are shown to vary systematically with a profiles fitted radial extent, and often by more than 100%. Considering elliptical galaxies spanning a range of 7.5 mag, we reveal that the central stellar densities of the underlying host galaxies increase with galaxy luminosity until the onset of core formation, detected only in the brightest elliptical galaxies. We suggest that the so-called power-law galaxies may actually be described by the Sersic model over their entire radial range.