Context. The physical and chemical conditions in Class 0/I protostars are fundamental in unlocking the protostellar accretion process and its impact on planet formation.Aims: The aim is to... Show moreContext. The physical and chemical conditions in Class 0/I protostars are fundamental in unlocking the protostellar accretion process and its impact on planet formation.Aims: The aim is to determine which physical components are traced by different molecules at subarcsecond scales (<100-400 au).Methods: We used a suite of Atacama Large Millimeter/submillimeter Array (ALMA) datasets in band 6 (1 mm), band 5 (1.8 mm), and band 3 (3 mm) at spatial resolutions 0.″5-3″ for 16 protostellar sources. For a subset of sources, Atacama Compact Array (ACA) data at band 6 with a spatial resolution of 6″ were added. The availability of low- and high-excitation lines and data on small and larger scales, is important to understand the full picture.Results: The protostellar envelope is well traced by C18O, DCO+, and N2D+, which stems from the freeze-out of CO governing the chemistry at envelope scales. Molecular outflows are seen in classical shock tracers such as SiO and SO, but ice-mantle products such as CH3OH and HNCO that are released with the shock are also observed. The molecular jet is a key component of the system. It is only present at the very early stages, and it is prominent not only in SiO and SO, but occasionally also in H2CO. The cavity walls show tracers of UV-irradiation such as C2H, c-C3H2 and CN. In addition to showing emission from complex organic molecules (COMs), the hot inner envelope also presents compact emission from small molecules such as H2S, SO, OCS, and H13CN, which most likely are related to ice sublimation and high-temperature chemistry.Conclusions: Subarcsecond millimeter-wave observations allow us to identify these (simple) molecules that best trace each of the physical components of a protostellar system. COMs are found both in the hot inner envelope (high-excitation lines) and in the outflows (lower-excitation lines) with comparable abundances. COMs can coexist with hydrocarbons in the same protostellar sources, but they trace different components. In the near future, mid-infrared observations with JWST-MIRI will provide complementary information about the hottest gas and the ice-mantle content, at unprecedented sensitivity and at resolutions comparable to ALMA for the same sources. Show less
We investigate the specific angular momentum (sAM) j((star)((star) proportional to M-star(alpha) with an index alpha varying from alpha = 0.3 to alpha = 0.5, from log M-star/M-circle dot = 8 to log... Show moreWe investigate the specific angular momentum (sAM) j((star)((star) proportional to M-star(alpha) with an index alpha varying from alpha = 0.3 to alpha = 0.5, from log M-star/M-circle dot = 8 to log M-star/M-circle dot = 10.5. The UDF sample supports a redshift evolution (j) over tilde (star proportional to) (1 + z)(a), with a = 0.27(-0.56)(+0.42) which is consistent with the (1 + z)(-0.5) expectation from a universe in expansion. The scatter of the sAM sequence is a strong function of the dynamical state with logj vertical bar(M star) proportional to 0.65(-0.08)(+0.06) x log(V-max/sigma), where sigma is the velocity dispersion at 2R(e). In TNG50, SFGs also form a (j) over tilde (star) - M-star (V/sigma) plane, but it correlates more with galaxy size than with morphological parameters. Our results suggest that SFGs might experience a dynamical transformation, and lose their sAM, before their morphological transformation to becoming passive via either merging or secular evolution. Show less
Context. The electron density (n) plays an important role in setting the chemistry and physics of the interstellar medium. However, measurements of n in neutral clouds have been directly obtained... Show moreContext. The electron density (n) plays an important role in setting the chemistry and physics of the interstellar medium. However, measurements of n in neutral clouds have been directly obtained only toward a few lines of sight or they rely on indirect determinations. Aims. We use carbon radio recombination lines and the far-infrared lines of C to directly measure neand the gas temperature in the envelope of the integral shaped filament (ISF) in the Orion A molecular cloud. Methods. We observed the C102 alpha (6109.901 MHz) and C109 alpha (5011.420 MHz) carbon radio recombination lines (CRRLs) using the Effelsberg 100 m telescope at approximate to 2 ' resolution toward five positions in OMC-2 and OMC-3. Since the CRRLs have similar line properties, we averaged them to increase the signal-to-noise ratio of the spectra. We compared the intensities of the averaged CRRLs, and the 158 mu m-[CII] and [(CII)-C-13] lines to the predictions of a homogeneous model for the C/C interface in the envelope of a molecular cloud and from this comparison we determined the electron density, temperature and C column density of the gas. Results. We detect the CRRLs toward four positions, where their velocity (v approximate to 11 km s) and widths (sigma v approximate to 1 km s) confirms that they trace the envelope of the ISF. Toward two positions we detect the CRRLs, and the 158 mu m-[CII] and [13CII] lines with a signal-to-noise ratio >= 5, and we find ne= 0.65 +/- 0.12 cm-3 and 0.95 +/- 0.02 cm(-3), which corresponds to a gas density nH approximate to 5 x 10(3) cm(-3) and a thermal pressure of p approximate to 4 x 10. We also constrained the ionization fraction in the denser portions of the molecular cloud using the HCN(1-0) and CH(1-0) lines to x(e) <= 3 x 10. Conclusions. The derived electron densities and ionization fraction imply that x(e) drops by a factor >= 100 between the Clayer and the regions probed by HCN(1-0). This suggests that electron collisional excitation does not play a significant role in setting the excitation of HCN(1-0) toward the region studied, as it is responsible for only approximate to 10% of the observed emission. Show less
Strong accretion shocks are expected to illuminate the warm-hot intergalactic medium encompassed by the filaments of the cosmic web, through synchrotron radio emission. Given their high sensitivity... Show moreStrong accretion shocks are expected to illuminate the warm-hot intergalactic medium encompassed by the filaments of the cosmic web, through synchrotron radio emission. Given their high sensitivity, large low-frequency radio facilities may already be able to detect signatures of this extended radio emission from the region between two close and massive galaxy clusters. In this work we exploit the non-detection of such diffuse emission by deep observations of two pairs of relatively close (similar or equal to 10 Mpc) and massive (M-500 >= 10(14) M-circle dot) galaxy clusters using the LOw-Frequency ARray. By combining the results from the two putative inter-cluster filaments, we derive new independent constraints on the median strength of intergalactic magnetic fields: B-10Mpc < 2.5 x 10(2) nG (95% confidence level). Based on cosmological simulations and assuming a primordial origin of the B-fields, these estimates can be used to limit the amplitude of primordial seed magnetic fields: B-0 <= 10 nG. We recommend the observation of similar cluster pairs as a powerful tool to set tight constraints on the amplitude of extragalactic magnetic fields. Show less
Terwisscha van Scheltinga, J.; Marcandalli, G.; McClure, M.K.; Hogerheijde, M.R.; Linnartz, H. 2021
Context. Infrared spectroscopy of star and planet forming regions is at the dawn of a new age with the upcoming James Webb Space Telescope (JWST). Its high resolution and unprecedented sensitivity... Show moreContext. Infrared spectroscopy of star and planet forming regions is at the dawn of a new age with the upcoming James Webb Space Telescope (JWST). Its high resolution and unprecedented sensitivity allows us to probe the chemical complexity of planet forming regions, such as dense clouds, embedded protostars, and protoplanetary disks, both in the solid state and gas phase. In support of these observations, laboratory spectra are required to identify complex organic molecules in the ices that cover the dust grains in these regions.Aims. This study aims to provide the necessary reference spectra to firmly detect methyl formate (HCOOCH3) in the different evolutionary stages of star and planet forming regions. Methyl formate is mixed in astronomically relevant matrices, and the peak positions, full width at half maximum, and relative band intensities are characterized for different temperatures to provide an analytical tool for astronomers.Methods. Methyl formate was deposited at 15 Kelvin on a cryogenically cooled infrared transmissive window under high-vacuum conditions. Specifically, methyl formate was deposited pure and mixed with CO, H2CO, CH3OH, H2O, and CO:H2CO:CH3OH combined. The sample was linearly heated until all solid-state constituents were desorbed. Throughout the experiment, infrared spectra were acquired with a Fourier transform infrared spectrometer in the range from 4000 to 500 cm(-1) (2.5-20 mu m) at a spectral resolution of 0.5 cm(-1).Results. We present the characterization of five solid-state methyl formate vibrational modes in pure and astronomically relevant ice matrices. The five selected vibrational modes, namely the C=O stretch (5.804 mu m), the C-O stretch (8.256 mu m), CH3 rocking (8.582 mu m), O-CH3 stretching (10.98 mu m), and OCO deformation (13.02 mu m), are best suited for a JWST identification of methyl formate. For each of these vibrational modes, and each of the mixtures the temperature versus spectra heatmaps, peak position versus full width at half maximum and relative band intensities are given. All spectra are publicly available on the Leiden Ice Database. Additionally, the acquired reference spectra of methyl formate are compared with archival Spitzer observations of HH 46. A tentative detection of methyl formate provides an upper limit to the column density of 1.7 x 10(17) cm(-2), corresponding to an upper limit relative to water of <= 2.2% and <= 40% with respect to methanol. Show less
Morganti, R.; Oosterloo, T.A.; Brienza, M.; Jurlin, N.; Prandoni, I.; Orru, E.; ... ; Ziemke, J. 2021
Super massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding... Show moreSuper massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of the images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of similar to 15 arcsec) for all the sources within an approximately 6 deg(2) area of the Lockman Hole region. In this way, we were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent cases of radio sources in the remnant or the restarted phases of their life cycle. Our findings confirm that these objects are not as rare as previously thought, suggesting a relatively fast cycle. They also show a variety of properties that can be relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the "off" (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with the results of simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), possibly suggesting different types of progenitors. The present work sets the stage for exploiting the powerful tool of low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys. Show less
Balmaverde, B.; Capetti, A.; Marconi, A.; Venturi, G.; Chiaberge, M.; Baldi, R.D.; ... ; Tremblay, G. 2021
