Aims. We examine the interstellar medium (ISM) of M 33 to unveil fingerprints of self-gravitating gas clouds throughout the star-forming disk. Methods. The probability distribution functions (PDFs) ...for atomic, molecular, and total gas surface densities are determined at a resolution of about 50 pc over regions that share coherent morphological properties and considering cloud samples at different evolutionary stages in the star formation cycle. Results. Most of the total gas PDFs are well fit by log-normal functions whose width decreases radially outward. Because the HI velocity dispersion is approximately constant throughout the disk, the decrease in PDF width is consistent with a lower Mach number for the turbulent ISM at large galactocentric radii where a higher fraction of HI is in the warm phase. The atomic gas is found mostly at face-on column densities below NHlim = 2.5 × 1021 cm−2NHlim=2.5×1021 cm−2$N_{\rm{H}}^{{\lim}} = 2.5 \times {10^{21}} \ {\rm{c}}{{\rm{m}}^{- 2}}$, with small radial variations of NHlimNHlim$N_{\rm{H}}^{{\lim}}$. The molecular gas PDFs do not show strong deviations from log-normal functions in the central region where molecular fractions are high. Here the high pressure and rate of star formation shapes the PDF as a log-normal function, dispersing self-gravitating complexes with intense feedback at all column densities that are spatially resolved. Power-law PDFs for the molecules are found near and above NHlimNHlim$N_{\rm{H}}^{{\lim}}$, in the southern spiral arm and in a continuous dense filament extending at larger galactocentric radii. In the filament nearly half of the molecular gas departs from a log-normal PDF, and power laws are also observed in pre-star-forming molecular complexes. The slope of the power law is between −1 and −2. This slope, combined with maps showing where the different parts of the power law PDFs come from, suggests a power-law stratification of the density within molecular cloud complexes, in agreement with the dominance of self-gravity.
Aims. We investigate a possible close encounter between M33 and M31 in the past to understand the role of galaxy-galaxy interactions in shaping the matter distribution in galaxy outskirts. Methods. ...By examining a variety of initial conditions, we recovered possible orbital trajectories of M33, M31, and the Milky Way in the past, which are compatible with the Early Third Data Release of the Gaia mission and with mass estimates of Local Group spirals. Using test-particle simulations, we explored if the M33 warp and its dark satellite distribution have been induced by a past M33–M31 encounter along these orbits, after tuning mass losses and the dynamical friction term with the help of N -body numerical simulations. Results. A close encounter of M33 and M31 in the past has a low but non-negligible probability. If the two galaxies had been closer in the past, their minimum distance would be of the order of 100 kpc or larger, and this happened earlier than 3 Gyr ago. During this encounter, 35–40% of the dark matter mass of M33 might have been removed from the halo due to tidal stripping. A detailed comparison of the results of test-particle simulations with the observed disk warp or with the spatial distribution of candidate dark satellites of M33 suggests that a closer passage of M33 around M31 cannot, however, be responsible for the observed morphological features. We suggest that more recent gas accretion events, possibly from a cosmic filament, might cause the misalignment of the outer disk of M33 after the rapid inner disk formation.
The relationship between the star formation rate and surface density of neutral gas within the disk of M33 is examined with new imaging observations of super(12)CO J = 1-0 emission gathered with the ...Five College Radio Astronomy Observatory (FCRAO) 14 m telescope and IRAS HiRes images of the 60 and 100 mu m emission. The Schmidt law, capital sigma sub(SFR) approx capital sigma image, is constructed using radial profiles of the H I 21 cm, CO, and far-infrared emission. We identify a strong correlation between the star formation rate and molecular gas surface density. This suggests that the condensation of giant molecular clouds (GMCs) is the limiting step to star formation within the M33 disk. The corresponding molecular Schmidt index, n sub(mol), is 1.36 plus or minus 0.08. The star formation rate has a steep dependence on total mass gas surface density, ( capital sigma image + capital sigma image), owing to the shallow radial profile of the atomic gas that dominates the total gas surface density for most radii. The disk pressure of the gas is shown to play a prominent role in regulating the molecular gas fraction in M33.
Una gigantesca nube di gas con massa equivalente a quella di una galassia, ma senza un'estesa controparte stellare, si estende nello spazio intergalattico vicino a noi. Recenti osservazioni ...spettroscopiche hanno individuato in questa struttura rare stelle giovani di grande massa la cui radiazione riscalda il gas circostante rivelando in esso le impronte di elementi pesanti. Le abbondanze chimiche di questi elementi hanno implicazioni profonde sull'origine di questa nube, una questione discussa ormai da quasi 40 anni. Parole chiave. Mezzo intergalattico, regioni HII, galassie.
The origin of the most extended intergalactic cloud of the local Universe, the Leo ring, has been debated for about 40 years. It has a gas mass equivalent to that of a galaxy but no extended optical ...counterpart. Recent observations with integral field spectroscopy have localized small star formation sites with young, massive stars in the cloud. The light from the hot gas in their proximity has the footprints of heavy elements with abundances close to solar ones, unveiling the long-standing mystery of the origin of this giant ring.
Aims. We determine the mass distribution of stars, gas, and dark matter in M 33 to test cosmological models of galaxy formation and evolution. Methods. We map the neutral atomic gas content of M 33 ...using high resolution Very Large Array and Green Bank Telescope observations of the 21 cm HI line emission. A tilted ring model is fitted to the HI datacube to determine the varying spatial orientation of the extended gaseous disk and the rotation curve. We derive the stellar mass surface density map of M 33’s optical disk via pixel-SED fitting methods based on population synthesis models that allow for positional changes in star formation history. Stellar and gas maps are used in the dynamical analysis of the rotation curve to constrain the dark halo properties. Results. The disk of M 33 warps from 8 kpc outward without substantial change of its inclination with respect to the line of sight; the line of nodes rotates clockwise toward the direction of M 31. Rotational velocities rise steeply with radius in the inner disk, reaching 100 km s-1 in 4 kpc, then the rotation curve becomes more perturbed and flatter with velocities as high as 120–130 km s-1 out to 2.7 R25. The stellar surface density map highlights a star-forming disk with a varying mass-to-light ratio. At larger radii, a dynamically relevant fraction of the baryons are in gaseous form. A dark matter halo with a Navarro-Frenk-White density profile, as predicted by hierarchical clustering and structure formation in a ΛCDM cosmology, provides the best fits to the rotation curve. Dark matter is relevant at all radii in shaping the rotation curve and the most likely dark halo has a concentration C ≃ 9.5 and a total mass of 4.3(±1.0) × 1011 M⊙. This imples a baryonic fraction of order 0.02 and the evolutionary history of this galaxy should therefore account for loss of a large fraction of its original baryonic content.
Il personale dell'INAF-Osservatorio di Arcetri ha sempre contribuito a creare itinerari ed eventi per la comunicazione della scienza. Gli innumerevoli incontri con il pubblico e con le scuole sono ...non solo strumenti per la diffusione della cultura astronomica, ma anche momenti di crescita collettiva, di condivisione di quell'incanto e stupore che si prova davanti alle meraviglie del cielo. Parole chiave. Comunicazione della scienza, gioco, spettacolo, didattica, licei scientifici Over the years, the staff of the INAF-Osservatorio di Arcetri has always planned new opportunities and events for public outreach and education. Countless meetings and events with the public and with students are not only tools for disseminating astronomy, but also moments of collective growth, thanks to the sharing of that enchantment and wonder that each of us feels when we look at the sky. Keywords. Science communication, games, public performances, education, high schools, astronomy.
Over the years, the staff of the INAF-Osservatorio di Arcetri has always planned new opportunities and events for public outreach and education. Countless meetings and events with the public and with ...students are not only tools for disseminating astronomy, but also moments of collective growth, thanks to the sharing of that enchantment and wonder that each of us feels when we look at the sky
We carried out deep searches for CO line emission in the outer disk of M 33, at R > 7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular ...cloud throughout the disk of M 33. We used the IRAM-30 m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M 33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M 33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R > 7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7 ± 0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.
Aims.
We carried out sensitive searches for the
12
CO
J
= 1–0 and
J
= 2–1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas ...metallicities are close to solar, but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations.
Methods.
We used the IRAM-30 m telescope to observe 11 regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached spectral noise between 1 and 5 mK for at least one of the observed frequencies at 2 km s
−1
spectral resolution.
Results.
We marginally detect two
12
CO
J
= 1–0 lines in the star-forming region Clump 1 of the Leo ring, whose radial velocities are consistent with those of H
α
lines, but whose line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths, and the extremely low number densities inferred by virialized cloud models suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt–Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.
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