E. Mármol-Queraltó

CALIFA, the Calar Alto Legacy Integral Field Area survey

We present the Calar Alto Legacy Integral Field Area survey (CALIFA). CALIFAs main aim is to obtain spatially resolved spectroscopic information for ~600 galaxies of all Hubble types in the Local Universe (0.005< z <0.03). The survey has been designed to allow three key measurements to be made: (a) Two-dimensional maps of stellar populations (star formation histories, chemical elements); (b) The distribution of the excitation mechanism and element abundances of the ionized gas; and (c) Kinematic properties (velocity ?elds, velocity dispersion), both from emission and from absorption lines. To cover the full optical extension of the target galaxies (i.e. out to a 3sigma depth of ~23 mag/arcsec2), CALIFA uses the exceptionally large ?eld of view of the PPAK/PMAS IFU at the 3.5m telescope of the Calar Alto observatory. We use two grating setups, one covering the wavelength range between 3700 and 5000 AA at a spectral resolution R~1650, and the other covering 4300 to 7000 AA at R~850. The survey was allocated 210 dark nights, distributed in 6 semesters and starting in July 2010 and is carried out by the CALIFA collaboration, comprising ~70 astronomers from 8 di?erent countries. As a legacy survey, the fully reduced data will be made publically available, once their quality has been veri?ed. We showcase here early results obtained from the data taken so far (21 galaxies).

The ASTRODEEP Frontier Fields catalogues - II. Photometric redshifts and rest frame properties in Abell-2744 and MACS-J0416

Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to cluster members themselves. Methods. We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC, which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six different approaches to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts. Results. We show that photometric redshifts reach a remarkable ~3–5% accuracy. After accounting for magnification, the H-band number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending the presently available samples to galaxies that, intrinsically, are as faint as H ~ 32−33, thanks to strong gravitational lensing. The Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with respect to extragalactic wide fields, including sources at M_(star) ~ 10^7–10^8 M_⊙ at z > 5. Similarly, they allow the detection of objects with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M_⊙/yr at z ~ 6–10.

Constraints on the merging channel of massive galaxies since z ∼ 1

We probe the merging channel of massive galaxies over the z= 0.3 − 1.3 redshift window by studying close pairs in a sample of 238 galaxies with stellar mass >∼ 1011M⊙, from the SHARDS survey. SHARDS provides medium band photometry equivalent to low-resolution optical spectra (R∼50), allowing us to obtain extremely accurate photometric redshifts (median |∆z|/(1 + z) ∼ 0.55%) and to improve the constraints on the age distribution of the stellar populations. Our dataset is volume-limited, probing merger progenitors with mass ratios 1:100 (µ ≡ Msat/Mcen = 0.01) out to z=1.3. A strong correlation is found between the age difference of host and companion galaxy and stellar mass ratio, from negligible age differences in major mergers to age differences ∼4 Gyr for 1:100 minor mergers. However, this correlation is simply a reflection of the mass-age trend in the general population. The dominant contributor to the growth of massive galaxies corresponds to mass ratios µ >∼ 0.3, followed by a decrease in the fractional mass growth rate linearly proportional to log µ, at least down to µ ∼ 0.01, suggesting a decreasing role of mergers involving lowmass companions, especially if dynamical friction timescales are taken into account. A simple model results in an upper limit for the average mass growth rate of massive galaxies of (∆M/M)/∆t ∼ 0.08 ± 0.02 Gyr−1 , over the z ∼ 0.3. The majority of the stellar mass contributed by mergers does not introduce significantly younger populations, in agreement with the small radial age gradients observed in present-day early-type galaxies.

The effects of spatial resolution on integral field spectrograph surveys at different redshifts - The CALIFA perspective

Context. Over the past decade, 3D optical spectroscopy has become the preferred tool for understanding the properties of galaxies and is now increasingly used to carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass, ATLAS3D, PINGS, and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS, GLACE, and IMAGES have targeted the most luminous galaxies to study mainly their kinematic properties. The on-going CALIFA survey (z ∼ 0.02) is the first of a series of upcoming integral field spectroscopy (IFS) surveys with large samples representative of the entire population of galaxies. Others include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at higher redshift. Given the importance of spatial scales in IFS surveys, the study of the effects of spatial resolution on the recovered parameters becomes important. Aims. We explore the capability of the CALIFA survey and a hypothetical higher redshift survey to reproduce the properties of a sample of objects observed with better spatial resolution at lower redshift. Methods. Using a sample of PINGS galaxies, we simulated observations at different redshifts. We then studied the behaviour of different parameters as the spatial resolution degrades with increasing redshift. Results. We show that at the CALIFA resolution, we are able to measure and map common observables in a galaxy study: the number and distribution of H ii regions (Hα flux structure), the gas metallicity (using the O3N2 method), the gas ionization properties (through the [N ii]/Hα and [O iii]/Hβ line ratios), and the age of the underlying stellar population (using the D4000 index). This supports the aim of the survey to characterise the observable properties of galaxies in the Local Universe. Our analysis of simulated IFS data cubes at higher redshifts highlights the importance of the projected spatial scale per spaxel as the most important figure of merit in the design of an integral field survey.

The evolution of the equivalent width of the Hα emission line and specific star formation rate in star-forming galaxies at 1 < z < 5

We present the results of a study which uses spectral energy distribution (SED) fitting to investigate the evolution of the equivalent width (EW) of the Halpha emission line in star-forming galaxies over the redshift interval 1 =1 in the CANDELS UDS and GOODS-S fields. Confining our analysis to a constant stellar mass range (9.5<log(M/Msun)<10.5), we find that the median EW(Ha) evolves only modestly with redshift, reaching a rest-frame value of EW(Ha)=301+/-30 Angs by redshift z~4.5. Furthermore, using estimates of star-formation rate (SFR) based on both UV luminosity and Ha line flux, we use our galaxy samples to compare the evolution of EW(Ha) and specific star-formation rate (sSFR). Our results indicate that over the redshift range 1<z<5, the evolution displayed by EW(Ha) and sSFR is consistent, and can be adequately parameterized as: propto (1+z)^(1.0+/-0.2). As a consequence, over this redshift range we find that the sSFR and rest-frame EW(Ha) of star-forming galaxies with stellar masses M~10^(10) Msun are related by: EW(Ha)/Ang=(63+/-7)sSFR/Gyr^(-1). Given the current uncertainties in measuring the SFRs of high-redshift galaxies, we conclude that EW(Ha) provides a useful independent tracer of sSFR for star-forming galaxies out to redshifts of z=5.

Non-parametric analysis of the rest-frame UV sizes and morphological disturbance amongst L* galaxies at 4 < z < 8

We present the results of a study investigating the sizes and morphologies of redshift 4 < z < 8 galaxies in the CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) GOODS-S (Great Observatories Origins Deep Survey southern field), HUDF (Hubble Ultra-Deep Field) and HUDF parallel fields. Based on non-parametric measurements and incorporating a careful treatment of measurement biases, we quantify the typical size of galaxies at each redshift as the peak of the lognormal size distribution, rather than the arithmetic mean size. Parametrizing the evolution of galaxy half-light radius as r_(50) ∝ (1 + z)^n, we find n = −0.20 ± 0.26 at bright UV-luminosities (0.3L_*(z = 3) < L < L_*) and n = −0.47 ± 0.62 at faint luminosities (0.12L_* < L < 0.3L_*). Furthermore, simulations based on artificially redshifting our z ∼ 4 galaxy sample show that we cannot reject the null hypothesis of no size evolution. We show that this result is caused by a combination of the size-dependent completeness of high-redshift galaxy samples and the underestimation of the sizes of the largest galaxies at a given epoch. To explore the evolution of galaxy morphology we first compare asymmetry measurements to those from a large sample of simulated single Sersic profiles, in order to robustly categorize galaxies as either ‘smooth’ or ‘disturbed’. Comparing the disturbed fraction amongst bright (M_(1500) ≤ −20) galaxies at each redshift to that obtained by artificially redshifting our z ∼ 4 galaxy sample, while carefully matching the size and UV-luminosity distributions, we find no clear evidence for evolution in galaxy morphology over the redshift interval 4 < z < 8. Therefore, based on our results, a bright (M_(1500) ≤ −20) galaxy at z ∼ 6 is no more likely to be measured as ‘disturbed’ than a comparable galaxy at z ∼ 4, given the current observational constraints.

Satellites around massive galaxies since z∼ 2

The accretion of minor satellites has been postulated as the most likely mechanism to explain the significant size evolution of massive galaxies over cosmic time. Using a sample of 629 massive (M_star~ 10^11 M_⊙) galaxies from the near-infrared Palomar/DEEP-2 survey, we explore what fraction of these objects have satellites with 0.01 < M_sat/M_central < 1 (1:100) up to z= 1 and what fraction have satellites with 0.1 < M_sat/M_central < 1 (1:10) up to z= 2 within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites, after background correction, remains basically constant and close to 30 per cent for satellites with a mass ratio down to 1:100 up to z= 1, and close to 15 per cent for satellites with a 1:10 mass ratio up to z= 2. The family of spheroid-like massive galaxies presents a 2–3 times larger fraction of objects with satellites than the group of disc-like massive galaxies. A crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy has experienced since z~2 is around 2. For a disc-like galaxy this number decreases to ~1.

A new stellar library in the region of the CO index at 2.3 mu m - New index definition and empirical fitting functions

Context. The analysis of unresolved stellar populations demands evolutionary synthesis models with realistic physical ingredients and extended wavelength coverage. Aims. We quantitatively describe the first CO bandhead at 2.3 mu m to allow stellar population models to provide improved predictions in this wavelength range. Methods. We observed a new stellar library with a better coverage of the stellar atmospheric parameter space than in earlier works. We performed a detailed analysis of the robustness of previous CO index definitions with spectral resolution, wavelength calibration, signal-to-noise ratio, and flux calibration. Results. We define a new line-strength index for the first CO bandhead at 2.3 mu m, DCO, better suited for stellar population studies than previous index definitions. We derive empirical fitting functions for the CO feature as a function of the stellar parameters (T(eff), log g and [Fe/H]), showing a detailed quantitative metallicity dependence.

The Mice at play in the CALIFA survey - A case study of a gas-rich major merger between first passage and coalescence

We present optical integral field spectroscopy (IFS) observations of the Mice, a major merger between two massive (≳10^11 M_⊙) gas-rich spirals NGC 4676A and B, observed between first passage and final coalescence. The spectra provide stellar and gas kinematics, ionised gas properties, and stellar population diagnostics, over the full optical extent of both galaxies with ~1.6 kpc spatial resolution. The Mice galaxies provide a perfect case study that highlights the importance of IFS data for improving our understanding of local galaxies. The impact of first passage on the kinematics of the stars and gas has been significant, with strong bars most likely induced in both galaxies. The barred spiral NGC 4676B exhibits a strong twist in both its stellar and ionised gas disk. The edge-on disk galaxy NGC 4676A appears to be bulge free, with a strong bar causing its “boxy” light profile. On the other hand, the impact of the merger on the stellar populations has been minimal thus far. By combining the IFS data with archival multiwavelength observations we show that star formation induced by the recent close passage has not contributed significantly to the total star formation rate or stellar mass of the galaxies. Both galaxies show bicones of high ionisation gas extending along their minor axes. In NGC 4676A the high gas velocity dispersion and Seyfert-like line ratios at large scaleheight indicate a powerful outflow. Fast shocks (vs ~ 350 km s^-1) extend to ~6.6 kpc above the disk plane. The measured ram pressure (P/k = 4.8 × 10^6 K cm^-3) and mass outflow rate (~8−20 M_⊙ yr^-1) are similar to superwinds from local ultra-luminous infrared galaxies, although NGC 4676A only has a moderate infrared luminosity of 3 × 10^10 L_⊙. Energy beyond what is provided by the mechanical energy of the starburst appears to be required to drive the outflow. Finally, we compare the observations to mock kinematic and stellar population maps extracted from a hydrodynamical merger simulation. The models show little enhancement in star formation during and following first passage, in agreement with the observations. We highlight areas where IFS data could help further constrain the models.

Satellite galaxies around present-day massive ellipticals

Using the spectroscopic New York University Value-Added Galaxy Catalogue and the photometric photo-z catalogues of the Sloan Digital Sky Survey Data Release 7, we have explored the satellite distribution around ~1000 massive (M_star > 2x10^11 M_sun) visually classified elliptical galaxies down to a satellite mass ratio of 1:400 (i.e. 5x10^8