M. D. Lehnert

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).

Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326: Evidence for negative AGN feedback

We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation nrate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency nis likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry nwith existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors n10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of n3C 326 N in the optical suggests an outflow with a terminal velocity of ~−1800 km s^(−1) and a mass outflow rate of 30−40 M_⊙ yr^(−1), nwhich cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the nbolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where na small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, nand the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times nare of order 10^(7−8) yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2 nluminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies nin a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of n≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback.

CO line emission in the halo of a radio galaxy at z = 2.6

We report the detection of luminous CO(3-2) line emission in the halo of the z = 2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at optical to mid-infrared wavelengths implying a stellar mass less than or similar to few x 10(9) M-circle dot and relatively low star formation rates. With the IRAM Plateau de Bure Interferometer (PdBI), we find two CO emission-line components at the same position at similar to 80 kpc distance from the HzRG along the axis of the radio jet, with different blueshifts of few 100 km s(-1) relative to the HzRG and a total luminosity of similar to 2 x 10(10) K km s(-1) pc(2) detected at a total significance of similar to 8 sigma. HzRGs have significant galaxy overdensities and extended haloes of metal-enriched gas often with embedded clouds or filaments of denser material, and likely trace very massive dark matter haloes. The CO emission may be associated with a gas-rich, low-mass satellite galaxy with very little ongoing star formation, in contrast to all previous CO detections of galaxies at similar redshifts. Alternatively, the CO may be related to a gas cloud or filament and perhaps jet-induced gas cooling in the outer halo, somewhat in analogy with extended CO emission found in low-redshift galaxy clusters.

A SINFONI view of flies in the spiderweb: a galaxy cluster in the making

The environment of the high-z radio galaxy PKS 1138-262 at z ∼ 2.2 is a prime example of a forming galaxy cluster. We use deep Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) integral field spectroscopy to perform a detailed study of the kinematics of the galaxies within 60 kpc of the radio core and we link this to the kinematics of the protocluster on the megaparsec scale. Identification of optical emission lines shows that 11 galaxies are at the redshift of the protocluster. The density of line emitters is more than an order of magnitude higher in the core of the protocluster with respect to the larger scale environment. This implies a galaxy overdensity in the core of δ g ∼ 200 and a matter overdensity of δ m ∼ 70; the latter is similar to that of the outskirts of local galaxy clusters. The velocity distribution of the confirmed satellite galaxies shows a broad, double-peaked velocity structure with σ = 1360 ± 206 km s ―1 . A similar broad, double-peaked distribution was found in a previous study targeting the large-scale protocluster structure, indicating that a common process is acting on both small and large scales. Including all spectroscopically confirmed protocluster galaxies, a velocity dispersion of 1013 ± 87 km s ―1 is found. We show that the protocluster has likely decoupled from the Hubble flow and is a dynamically evolved structure. A comparison to the Millennium Simulation indicates that the protocluster velocity distribution is consistent with that of the most massive haloes at z ∼ 2, but we rule out that the protocluster is a fully virialized structure based on dynamical arguments and its X-ray luminosity. Comparison to merging haloes in the Millennium Simulation shows that the structure as observed in and around the Spiderweb galaxy is best interpreted as being the result of a merger between two massive haloes. We propose that the merger of two subclusters can result in an increase in star formation and active galactic nucleus activity in the protocluster core, therefore possibly being an important stage in the evolution of massive cD galaxies.

The black holes of radio galaxies during the Quasar Era : masses, accretion rates, and evolutionary stage

We present an analysis of the AGN broad-line regions of 6 powerful radio galaxies at z ∼ 2 (HzRGs), which is part of a study of a sample of 50 HzRGs with rest-frame optical imaging spectroscopy obtained at the VLT. In 6 galaxies we detect luminous (L(Hα) = few x 10 44 erg s ―1 ), spatially unresolved, broad (FWHM ≥ 10 000 km s ―1 ) Hα line emission from the nucleus (HαBLRs), consistent with broad-line regions of supermassive black holes with masses of few x 10 9 M ⊙ and accretion luminosities of a few percent of the Eddington luminosity. In two galaxies we also detect HβBLRs, suggesting relatively low extinction of A V ∼ 1 mag, which agrees with constraints from X-ray observations. Overall, we find HαBLRs in ∼20% of the galaxies where Hα is observed. By relating black hole and bulge mass, we find a possible offset towards higher black-hole masses of at most ∼0.6 dex relative to nearby galaxies at a given host mass, although each individual galaxy is within the scatter of the local relationship. If not entirely from systematic effects, this would then suggest that the masses of the host galaxies have increased by at most a factor ≈4 since z ∼ 2 relative to the black-hole masses, perhaps through accretion of satellite galaxies or because of a time lag between star formation in the host galaxy and AGN fueling. We also compare the radiative and mechanical energy output (from jets) of our targets with predictions of recent models of synthesis or grand unified AGN feedback, which postulate that AGN with similar radiative and mechanical energy output rates to those found in our HzRGs may be nearing the end of their period of active growth. We discuss evidence that they may reach this stage at the same time as their host galaxies.

Molecular gas in the halo fuels the growth of a massive cluster galaxy at high redshift

The massive Spiderweb galaxy is surrounded by molecular gas as it goes through its formation process. A massive galaxy forming from molecular gas The most massive galaxies gather their stars by merging with smaller galaxies and by accreting gas, which is then consumed during star formation. Emonts et al. investigated the Spiderweb Galaxy, a massive galaxy in the process of forming in the early universe, seen now as it was over 10 billion years ago (see the Perspective by Hatch). Radio observations of carbon monoxide revealed large quantities of molecular gas around the galaxy. The gas is not associated with the merger process but may have been recycled from earlier phases of galaxy formation. Science, this issue p. 1128; see also p. 1102 The largest galaxies in the universe reside in galaxy clusters. Using sensitive observations of carbon monoxide, we show that the Spiderweb galaxy—a massive galaxy in a distant protocluster—is forming from a large reservoir of molecular gas. Most of this molecular gas lies between the protocluster galaxies and has low velocity dispersion, indicating that it is part of an enriched intergalactic medium. This may constitute the reservoir of gas that fuels the widespread star formation seen in earlier ultraviolet observations of the Spiderweb galaxy. Our results support the notion that giant galaxies in clusters formed from extended regions of recycled gas at high redshift.

Limits on the molecular gas content of z ∼ 5 LBGs

We present limits on the molecular gas content of Lyman break galaxies (LBGs) at from observations targeting redshifted CO(1–0) and CO(2–1) line emission. We observed a single field containing eight spectroscopically confirmed LBGs, seven of which are contained within a narrow () redshift range and the eighth is at z= 5.2. No source was individually detected. Assuming the CO to H2 conversion factor for vigorous starbursts, we place upper limits on the molecular gas content of individual LBGs of M(H2) . From a stacking analysis combining all of the non-detections, the typical LBG has an H2 mass limit comparable to their stellar mass, . This limit implies that, given the star formation rates of these systems (measured from their UV emission), star formation could be sustained for at most Myr, similar to the typical ages of their stellar populations. The lack of a substantially larger reservoir of cold gas argues against the LBGs being UV-luminous superstarbursts embedded in much larger UV-dark systems and as a result increases the likelihood that at least those LBGs with multiple components are starbursts triggered by mergers. The sources responsible for re-ionization are expected to be starbursts similar to these systems, but with lower luminosities, masses and consequently with star formation time-scales far shorter than the recombination time-scale. If so, the ionized bubbles expected in the IGM during the re-ionization era will only infrequently have UV-luminous sources at their centres.

Constraining the thermal dust content of Lyman break galaxies in an overdense field at z≈ 5

We have carried out 870-μm observations in the J1040.7−1155 field, known to host an overdensity of Lyman break galaxies at z= 5.16 ± 0.05. We do not detect any individual source at the S870 μm= 3.0 mJy beam−1 (2σ) level. A stack of nine spectroscopically confirmed z > 5 galaxies also yields a non-detection, constraining the submillimetre flux from a typical galaxy at this redshift to S870 μm < 0.85 mJy, which corresponds to a mass limit Mdust < 1.2 × 108 M⊙ (2σ). This limits the mass of thermal dust in distant Lyman break galaxies to less than one-tenth of their typical stellar mass. We see no evidence for strong submillimetre galaxies associated with the ultraviolet-selected galaxy overdensity, but cannot rule out the presence of fainter, less massive sources.

Identifying clustering at high redshift through actively star-forming galaxies

Identifying galaxy clustering at high redshift (i.e. z > 1) is essential to our understanding of the current cosmological model. However, at increasing redshift, clusters evolve considerably in star formation activity and so are less likely to be identified using the widely used red-sequence method. Here we assess the viability of instead identifying high-redshift clustering using actively star-forming galaxies (submillimetre galaxies, SMGs, associated with overdensities of BzKs/LBGs). We perform both a 2D and 3D clustering analysis to determine whether or not true (3D) clustering can be identified where only 2D data are available. As expected, we find that 2D clustering signals are weak at best and inferred results are method dependent. In our 3D analysis, we identify 12 SMGs associated with an overdensity of galaxies coincident both spatially and in redshift – just 8 per cent of SMGs with known redshifts in our sample. Where an SMG in our target fields lacks a known redshift, their sight line is no more likely to display clustering than blank sky fields; prior redshift information for the SMG is required to identify a true clustering signal. We find that the strength of clustering in the volume around typical SMGs, while identifiable, is not exceptional. However, we identify a small number of highly clustered regions, all associated with an SMG. The most notable of these, surrounding LESS J033336.8−274401, potentially contains an SMG, a quasi stellar object (QSO) and 36 star-forming galaxies (a >20σ overdensity) all at z ∼ 1.8. This region is highly likely to represent an actively star-forming cluster and illustrates the success of using star-forming galaxies to select sites of early clustering. Given the increasing number of deep fields with large volumes of spectroscopy, or high quality and reliable photometric redshifts, this opens a new avenue for cluster identification in the young Universe.

Limits on dust emission from z similar to 5 LBGs and their local environments

We present 1.2 mm MAMBO-2 observations of a field which is overdense in Lyman break galaxies (LBGs) at z similar to 5. The field includes seven spectroscopically confirmed LBGs contained within a narrow (z = 4.95 +/- 0.08) redshift range and an eighth at z = 5.2. We do not detect any individual source to a limit of 1.6 mJy/beam (2 x rms). When stacking the flux from the positions of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these sources of 0.6 mJy/beam. This limit is consistent with far-infrared (FIR) imaging in other fields which are overdense in ultraviolet-bright galaxies at z similar to 5. Independently and combined, these limits constrain the FIR luminosity (8-1000 mu m) to a typical z similar to 5 LBG of L-FIR less than or similar to 3 x 10(11) L-circle dot, implying a dust mass of M-dust less than or similar to 10(8) M-circle dot (both assuming a grey body at 30 K). This LFIR limit is an order of magnitude fainter than the LFIR of lower redshift submillimetre sources (z similar to 13). We see no emission from any other sources within the field at the above-mentioned level. While this is not unexpected, given millimetre source counts, the clustered LBGs trace significant overdense large-scale structure in the field at z = 4.95. The lack of any such detection in either this or the previous work implies that massive, obscured star-forming galaxies may not always trace the same structures as overdensities of LBGs, at least on the length scale probed here. We briefly discuss the implications of these results for future observations with ALMA.