Jet-induced star formation in 3C 285 and Minkowski Object

How efficiently star formation proceeds in galaxies is still an open question. Recent studies suggest that AGN can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback has also been observed in a few radio galaxies (eg. Centaurus A). Here we present CO observations of 3C 285 and Minkowski Object (MO), which are examples of jet-induced star formation. A spot (named 09.6) aligned with the 3C 285 radio jet, at a projected distance of ~70 kpc from the galaxy centre, shows star formation, detected in optical emission. MO is located along the jet of NGC 541 and also shows star formation. To know the distribution of molecular gas along the jets is a way to study the physical processes at play in the AGN interaction with the intergalactic medium. We observed CO lines in 3C 285, NGC 541, 09.6 and MO with the IRAM-30m telescope. In the central galaxies, the spectra present a double-horn profile, typical of a rotation pattern, from which we are able to estimate the molecular gas density profile of the galaxy. The molecular gas appears to be in a compact reservoir. In addition, no kinematic signature of a molecular outflow is detected by the 30m-telescope. Interestingly, 09.6 and MO are not detected in CO. The cold gas mass upper limits are consistent with a star formation induced by the compression of dense ambient material by the jet. The depletion time scales are of the order of and even smaller than what is found in 3C 285, NGC 541 and local spiral galaxies (10^9 yr). The molecular gas surface density in 09.6 follows a Schmidt-Kennicutt law if the emitting region is very compact, while MO is found to have a much higher SFE (very short depletion time). Higher sensitivity and spatial resolution are necessary to detect CO in the spots of star formation, and map the emission in these jet-induced star forming regions.Comment: 9 pages, 10 figures, submitted to A&

The overmassive black hole in NGC 1277: new constraints from molecular gas kinematics

We report the detection of CO(1-0) emission from NGC 1277, a lenticular galaxy in the Perseus Cluster. NGC 1277 has previously been proposed to host an overmassive black hole (BH) compared to the galaxy bulge luminosity (mass), based on stellar-kinematic measurements. The CO(1-0) emission, observed with the IRAM Plateau de Bure Interferometer (PdBI) using both, a more compact (2.9-arcsec resolution) and a more extended (1-arcsec resolution) configuration, is likely to originate from the dust lane encompassing the galaxy nucleus at a distance of 0.9 arcsec (~320 pc). The double-horned CO(1-0) profile found at 2.9-arcsec resolution traces $1.5\times 10^8\ M_\odot$ of molecular gas, likely orbiting in the dust lane at $\sim 550\ \mathrm{km\ s^{-1}}$, which suggests a total enclosed mass of$\sim 2\times 10^{10}\ M_\odot$. At 1-arcsec resolution, the CO(1-0) emission appears spatially resolved along the dust lane in east-west direction, though at a low signal-to-noise ratio. In agreement with the previous stellar-kinematic measurements, the CO(1-0) kinematics is found to be consistent with an$\sim 1.7\times 10^{10}\ M_\odot$BH for a stellar mass-to-light ratio of$M/L_V=6.3$, while a less massive BH of$\sim 5\times 10^{9}\ M_\odot$is possible when assuming a larger$M/L_V=10$. While the molecular gas reservoir may be associated with a low level of star formation activity, the extended 2.6-mm continuum emission is likely to originate from a weak AGN, possibly characterized by an inverted radio-to-millimetre spectral energy distribution. Literature radio and X-ray data indicate that the BH in NGC 1277 is also overmassive with respect to the Fundamental Plane of BH activity.Comment: 15 pages, 13 figures; accepted for publication in MNRAS on 20 January 2016; updated version including minor changes and note added in proo

Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*

We present the first spectral energy distributions produced self-consistently by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical simulations, where radiative cooling is included in the dynamical calculation. As a case study, we focus on the accretion flow around the supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best constrained physical parameters. We compare the simulated spectra to the observational data of Sgr A* and explore the parameter space of our model to determine the effect of changing the initial magnetic field configuration, ion to electron temperature ratio T_i/T_e and the target accretion rate. We find the best description of the data for a mass accretion rate of ~ 1e-9 Msun/yr, and rapid spin (0.7 < a_* < 0.9). The submillimeter peak flux seems largely independent of initial conditions, while the higher energies can be very sensitive to the initial magnetic field configuration. Finally, we also discuss flaring features observed in some simulations, that may be due to artifacts of the 2D configuration.Comment: Submitted to MNRAS. 13 pages, 15 figure

Cold gas in group-dominant elliptical galaxies

We present IRAM 30m telescope observations of the CO(1-0) and (2-1) lines in a sample of 11 group-dominant elliptical galaxies selected from the CLoGS nearby groups sample. Our observations confirm the presence of molecular gas in 4 of the 11 galaxies at >4 sigma significance, and combining these with data from the literature we find a detection rate of 43+-14%, comparable to the detection rate for nearby radio galaxies, suggesting that group-dominant ellipticals may be more likely to contain molecular gas than their non-central counterparts. Those group-dominant galaxies which are detected typically contain ~2x10^8 Msol of molecular gas, and although most have low star formation rates (<1 Msol/yr) they have short depletion times, indicating that the gas must be replenished on timescales ~100 Myr. Almost all of the galaxies contain active nuclei, and we note while the data suggest that CO may be more common in the most radio-loud galaxies, the mass of molecular gas required to power the active nuclei through accretion is small compared to the masses observed. We consider possible origin mechanisms for the gas, through cooling of stellar ejecta within the galaxies, group-scale cooling flows, and gas-rich mergers, and find probable examples of each type within our sample, confirming that a variety of processes act to drive the build up of molecular gas in group-dominant ellipticals.Comment: 9 pages, 5 postscript figures, 4 tables, accepted by A&A. Revised throughout in response to referee's comments, including updates to Table 1 and Figure 4, and addition of Figure

Resolving the molecular gas around the lensed quasar RXJ0911.4+0551

We report on high angular resolution observations of the CO(7-6) line and millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8) quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO observations resolve the molecular disk of the source. Using a lens model based on HST observations we fit source models to the observed visibilities. We estimate a molecular disk radius of 1$\pm$0.2 kpc and an inclination of 69$\pm$6\deg, the continuum is more compact and is only marginally resolved by our observations. The relatively low molecular gas mass, $Mgas=(2.3\pm 0.5)\times 10^{9}$ Msolar, and far infrared luminosity, $LFIR=(7.2\pm 1.5) \times 10^{11}$ Lsolar, of this quasar could be explained by its relatively low dynamical mass, $Mdyn=(3.9\pm 0.9)\times 10^9$ Msolar. It would be a scaled-down version the QSOs usually found at high-z. The FIR and CO luminosities lie on the correlation found for QSOs from low to high redshifts and the gas-to-dust ratio ($45\pm 17$) is similar to the one measured in the z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the continuum-to-line luminosity ratio, the line profile and possibly the spectral energy distribution.Comment: Accepted for publication in A&A, revised after language editin

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 rate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors 10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 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), which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times are 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 luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback

Sequence features of HLA-DRB1 locus define putative basis for gene conversion and point mutations

<p>Abstract</p> <p>Background</p> <p>HLA/MHC class II molecules show high degree of polymorphism in the human population. The individual polymorphic motifs have been suggested to be propagated and mixed by transfer of genetic material (recombination, gene conversion) between alleles, but no clear molecular basis for this has been identified as yet. A large number of MHC class II allele sequences is publicly available and could be used to analyze the sequence features behind the recombination, revealing possible basis for such recombination processes both in HLA class II genes and other genes, which recombination acts upon.</p> <p>Results</p> <p>In this study we analyzed the vast dataset of human allelic variants (49 full coding sequences, 374 full exon 2 sequences) of the most polymorphic MHC class II locus, <it>HLA-DRB1</it>, and identified many previously unknown sequence features possibly contributing to the recombination. The CpG-dinucleotide content of exon 2 (containing the antigen-binding sites and subsequently a high degree of polymorphism) was much elevated as compared to the other exons despite similar overall G+C content. Furthermore, the CpG pattern was highly conserved. We also identified more complex, highly conserved sequence motifs in exon 2. Some of these can be identified as putative recombination motifs previously found in other genes, but most are previously unidentified.</p> <p>Conclusion</p> <p>The identified sequence features could putatively act in recombination allowing either less (CpG dinucleotides) or more specific DNA cleavage (complex sequences) or homologous recombination (complex sequences).</p

Mapping the cold molecular gas in a cooling flow cluster: Abell 1795

Cold molecular gas is found in several clusters of galaxies (Edge, 2001, Salome' & Combes, 2003): single dish telescope observations in CO(1-0) and CO(2-1) emission lines have revealed the existence of large amounts of cold gas (up to ~10^11 Msol) in the central region of cooling flow clusters. We present here interferometric observations performed with the IRAM Plateau de Bure interferometer in Abell 1795. Comparison with IRAM 30m data shows the cold gas detected is extended suggesting a cooling flow origin. The CO features identified are very similar to the structures observed in Halpha and with the star forming regions observed through UV continuum excess. A large fraction of the cold gas is not centered on the central cD, but located near brightest X-ray emitting regions along the North-West orientated radio lobe. The cold gas kinematics is consistent with the optical nebulosity behaviour in the very central region. It is not in rotation around the central cD : a velocity gradient shows the cold gas might be cooled gas from the intra-cluster medium being accreted by the central galaxy. The optical filaments, aligned with the cD orbit, are intimately related to the radio jets and lobes. The material fueling the star formation certainly comes from the deposited gas, cooling more efficiently along the edge of the radio lobes. Even if some heating mechanisms are present, these millimetric observations show that an effective cooling to very low temperatures indeed occurs and is probably accelerated by the presence of the radio source.Comment: 4 pages, 4 figures, accepted for publication in A&A (Letter

Precursors’ order effect on the properties of sulfurized Cu2ZnSnS4 thin films

A dc magnetron sputtering-based method to grow high-quality Cu2ZnSnS4 (CZTS) thin films, to be used as an absorber layer in solar cells, is being developed. This method combines dc sputtering of metallic precursors with sulfurization in S vapour and with post-growth KCN treatment for removal of possible undesired Cu2−xS phases. In this work, we report the results of a study of the effects of changing the precursors’ deposition order on the final CZTS films’ morphological and structural properties. The effect of KCN treatment on the optical properties was also analysed through diffuse reflectance measurements. Morphological, compositional and structural analyses of the various stages of the growth have been performed using stylus profilometry, SEM/EDS analysis, XRD and Raman Spectroscopy. Diffuse reflectance studies have been done in order to estimate the band gap energy of the CZTS films. We tested two different deposition orders for the copper precursor, namely Mo/Zn/Cu/Sn and Mo/Zn/Sn/Cu. The stylus profilometry analysis shows high average surface roughness in the ranges 300–550 nm and 230–250 nm before and after KCN treatment, respectively. All XRD spectra show preferential growth orientation along (1 1 2) at 28.45◦. Raman spectroscopy shows main peaks at 338 cm−1 and 287 cm−1 which are attributed to Cu2ZnSnS4. These measurements also confirm the effectiveness of KCN treatment in removing Cu2−xS phases. From the analysis of the diffuse reflectance measurements the band gap energy for both precursors’ sequences is estimated to be close to 1.43 eV. The KCN-treated films show a better defined absorption edge; however, the band gap values are not significantly affected. Hot point probe measurements confirmed that CZTS had p-type semiconductor behaviour and C–V analysis was used to estimate the majority carrier density giving a value of 3.3 × 1018 cm−3

Growth and Raman scattering characterization of Cu2ZnSnS4 thin films

In the present work we report the results of the growth, morphological and structural characterization of Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence of the sulfurization temperature on the morphology, composition and structure of the films has been studied. With the presented method we have been able to prepare CZTS thin films with the kesterite structure