425 research outputs found
The star formation process on cloud-scales in nearby galaxies
No full textWhere do stars form and how is their formation regulated across galactic disks are two critical questions for our understanding of the star formation process. High angular observations of nearby galaxies allow us to sample the star formation process across entire galactic disks reaching now regularly the scales of the star-forming units, namely Giant Molecular Clouds (GMCs) and HII regions. These data provide new insights on the molecular gas reservoir and its role in the star formation process as well as information on the importance of galactic components such as bulges, stellar bars, spiral arms and active galactic nuclei (AGN) in the conversion of cold (molecular) gas into stars. ALMA is fundamental for studying the molecular gas properties while the optical Integral Field Unit MUSE on the VLT is providing detailed information on the ionised gas and stellar population.</p
Does the evolution of the radio luminosity function of star-forming galaxies match that of the star-formation rate function?
No full textThe assessment of the relationship between radio continuum luminosity and star formation rate (SFR) is of crucial importance to make reliable predictions for the forthcoming ultra-deep radio surveys and to allow a full exploitation of their results to measure the cosmic star formation history. We have addressed this issue by matching recent accurate determinations of the SFR function up to high redshifts with literature estimates of the 1.4 GHz luminosity functions of star forming galaxies (SFGs). This was done considering two options, proposed in the literature, for the relationship between the synchrotron emission (L_\rm synch), that dominates at 1.4 GHz, and the SFR: a linear relation with a decline of the L_\rm synch/SFR ratio at low luminosities or a mildly non-linear relation at all luminosities. In both cases we get good agreement with the observed radio luminosity functions but, in the non-linear case, the deviation from linearity must be small. The luminosity function data are consistent with a moderate increase of the L_\rm synch/SFR ratio with increasing redshift, indicated by other data sets, although a constant ratio cannot be ruled out. A stronger indication of such increase is provided by recent deep 1.4 GHz counts, down to Jy levels. This is in contradiction with models predicting a decrease of that ratio due to inverse Compton cooling of relativistic electrons at high redshifts. Synchrotron losses appear to dominate up to . We have also updated the Massardi et al. (2010) evolutionary model for radio loud AGNs. Copyright The Authors 201
Molecular Gas and the Star Formation Process on Cloud Scales in Nearby Galaxies
No full textObservations that resolve nearby galaxies into individual regions across
multiple phases of the gas-star formation-feedback ``matter cycle'' have
provided a sharp new view of molecular clouds, star formation efficiencies,
timescales for region evolution, and stellar feedback. We synthesize these
results, cover aspects relevant to the interpretation of observables, and
conclude that:
(1) The observed cloud-scale molecular gas surface density, line width, and
internal pressure all reflect the large-scale galactic environment while also
appearing mostly consistent with properties of a turbulent medium strongly
affected by self-gravity.
(2) Cloud-scale data allow for statistical inference of both evolutionary and
physical timescales. These suggest that clouds collapse on timescale of order
the free-fall or turbulent crossing time (~Myr) followed by the
formation of massive stars and subsequent rapid ( 5 Myr) gas
clearing. The star formation efficiency per free-fall time is well determined
over thousands of regions to be .
(3) The role of stellar feedback is now measured using multiple observational
approaches. The net momentum yield is constrained by the requirement to support
the vertical weight of the galaxy disk. Meanwhile, the short gas clearing
timescales suggest a large role for pre-supernova feedback in cloud disruption.
This leaves the supernovae free to exert a large influence on the larger scale
galaxy, including driving turbulence, launching galactic-scale winds, and
carving superbubbles.Comment: 70 pages, 15 figures, 9 tables. Authors' version of an article to
appear in Annual Reviews of Astronomy and Astrophysics 2024, Vol 6
Testing the evolutionary link between submillimetre galaxies and quasars: CO observations of QSOs at z~2
No full textWe have used the IRAM Plateau de Bure millimetre interferometer and the UKIRT 1–5 μm Imager Spectrometer (UIST) to test the connection between the major phases of spheroid growth and nuclear accretion by mapping CO emission in nine submillimetre-detected QSOs at z= 1.7–2.6 with black hole (BH) masses derived from near-infrared spectroscopy. When combined with one QSO obtained from the literature, we present sensitive CO(3–2) or CO(2–1) observations of 10 submillimetre-detected QSOs selected at the epoch of peak activity in both QSOs and submillimetre (submm) galaxies (SMGs). CO is detected in 5/6 very optically luminous (MB∼−28) submm-detected QSOs with BH masses MBH≃ 109–1010 M⊙, confirming the presence of large gas reservoirs of Mgas≃ 3.4 × 1010 M⊙. Our BH masses and dynamical mass constraints on the host spheroids suggest, at face value, that these optically luminous QSOs at z= 2 lie about an order of magnitude above the local BH–spheroid relation, MBH/Msph, although this result is dependent on the size and inclination of the CO-emitting region. However, we find that their BH masses are ∼30 times too large and their surface density is ∼300 times too small to be related to typical SMGs in an evolutionary sequence. Conversely, we measure weaker CO emission in four fainter (MB∼−25) submm-detected QSOs with properties, BH masses (MBH≃ 5 × 108 M⊙), and surface densities similar to SMGs. These QSOs appear to lie near the local MBH/Msph relation, making them plausible ‘transition objects’ in the proposed evolutionary sequence linking QSOs to the formation of massive young galaxies and BHs at high redshift. We show that SMGs have a higher incidence of bimodal CO line profiles than seen in our QSO sample, which we interpret as an effect of their relative inclinations, with the QSOs seen more face-on. Finally, we find that the gas masses of the four fainter submm-detected QSOs imply that their star formation episodes could be sustained for ∼10 Myr, and are consistent with representing a phase in the formation of massive galaxies which overlaps a preceding SMG starburst phase, before subsequently evolving into a population of present-day massive ellipticals
Magellan spectroscopy of AGN candidates in the COSMOS field
No full textWe present spectroscopic redshifts for the first 466 X-ray- and radio-selected AGN targets in the 2 deg2 COSMOS field. Spectra were obtained with the IMACS instrument on the Magellan (Baade) telescope, using the nod-and-shuffle technique. We identify a variety of type 1 and type 2 AGNs, as well as red galaxies with no emission lines. Our redshift yield is 72% down to iAB=24, although the yield is >90% for iAB<22. We expect the completeness to increase as the survey continues. When our survey is complete and additional redshifts from the zCOSMOS project are included, we anticipate ~1100 AGNs with redshifts over the entire COSMOS field. Our redshift survey is consistent with an obscured AGN population that peaks at z~0.7, although further work is necessary to disentangle the selection effects. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 and based on data collected at the Magellan Telescope, which is operated by the Carnegie Observatories
The impact of a young radio galaxy: clues from the cosmic ray electron population
No full textIn the framework of hierarchical structure formation, active galactic nuclei (AGN) feedback shapes the galaxy luminosity function. Low luminosity, galaxy-scale double radio sources are ideal targets to investigate the interplay between AGN feedback and star formation. We use Very Large Array and BIMA millimetre-wave array observations to study the radio continuum emission of NGC 3801 between 1.4 and 112.4 GHz. We find a prominent spectral break at ~10 GHz, where the spectrum steepens as expected from cosmic ray electron (CRe) ageing. Using the equipartition magnetic field and fitting JP models locally, we create a spatially resolved map of the spectral age of the CRe population. The spectral age of τint = 2.0 ± 0.2 Myr agrees within a factor of 2 with the dynamical age of the expanding X-ray emitting shells. The spectral age varies only little across the lobes, requiring an effective mixing process of the CRe such as a convective backflow of magnetized plasma. The jet termination points have a slightly younger CRe spectral age, hinting at in situ CRe re-acceleration. Our findings support the scenario where the supersonically expanding radio lobes heat the interstellar medium (ISM) of NGC 3801 via shock waves, and, as their energy is comparable to the energy of the ISM, are clearly able to influence the galaxy's further evolution
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