ABSTRACT
It is still poorly constrained how the densest phase of the interstellar medium varies across galactic environment. A large observing time is required to recover significant emission from ...dense molecular gas at high spatial resolution, and to cover a large dynamic range of extragalactic disc environments. We present new NOrthern Extended Millimeter Array (NOEMA) observations of a range of high critical density molecular tracers (HCN, HNC, HCO+) and CO isotopologues (13CO, C18O) towards the nearby (11.3 Mpc) strongly barred galaxy NGC 3627. These observations represent the current highest angular resolution (1.85 arcsec; 100 pc) map of dense gas tracers across a disc of a nearby spiral galaxy, which we use here to assess the properties of the dense molecular gas, and their variation as a function of galactocentric radius, molecular gas, and star formation. We find that the HCN(1–0)/CO(2–1) integrated intensity ratio does not correlate with the amount of recent star formation. Instead, the HCN(1–0)/CO(2–1) ratio depends on the galactic environment, with differences between the galaxy centre, bar, and bar-end regions. The dense gas in the central 600 pc appears to produce stars less efficiently despite containing a higher fraction of dense molecular gas than the bar ends where the star formation is enhanced. In assessing the dynamics of the dense gas, we find the HCN(1–0) and HCO+(1–0) emission lines showing multiple components towards regions in the bar ends that correspond to previously identified features in CO emission. These features are cospatial with peaks of Hα emission, which highlights that the complex dynamics of this bar-end region could be linked to local enhancements in the star formation.
Aims.
The complexity of star formation at the physical scale of molecular clouds is not yet fully understood. We investigate the mechanisms regulating the formation of stars in different environments ...within nearby star-forming galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) sample.
Methods.
Integral field spectroscopic data and radio-interferometric observations of 18 galaxies were combined to explore the existence of the resolved star formation main sequence (Σ
stellar
versus Σ
SFR
), resolved Kennicutt–Schmidt relation (Σ
mol. gas
versus Σ
SFR
), and resolved molecular gas main sequence (Σ
stellar
versus Σ
mol. gas
), and we derived their slope and scatter at spatial resolutions from 100 pc to 1 kpc (under various assumptions).
Results.
All three relations were recovered at the highest spatial resolution (100 pc). Furthermore, significant variations in these scaling relations were observed across different galactic environments. The exclusion of non-detections has a systematic impact on the inferred slope as a function of the spatial scale. Finally, the scatter of the Σ
mol. gas + stellar
versus Σ
SFR
correlation is smaller than that of the resolved star formation main sequence, but higher than that found for the resolved Kennicutt–Schmidt relation.
Conclusions.
The resolved molecular gas main sequence has the tightest relation at a spatial scale of 100 pc (scatter of 0.34 dex), followed by the resolved Kennicutt–Schmidt relation (0.41 dex) and then the resolved star formation main sequence (0.51 dex). This is consistent with expectations from the timescales involved in the evolutionary cycle of molecular clouds. Surprisingly, the resolved Kennicutt–Schmidt relation shows the least variation across galaxies and environments, suggesting a tight link between molecular gas and subsequent star formation. The scatter of the three relations decreases at lower spatial resolutions, with the resolved Kennicutt–Schmidt relation being the tightest (0.27 dex) at a spatial scale of 1 kpc. Variation in the slope of the resolved star formation main sequence among galaxies is partially due to different detection fractions of Σ
SFR
with respect to Σ
stellar
.
Syracuse and the other cities of the Hyblaean area (in south-eastern Sicily) are characterized by a close relationship between building stone and geological context, since the wide use of local ...calcarenites characterized and defined their urban planning and architecture.
In this paper, we discuss the results of a research aimed at investigating four types of limestone used in the built heritage of Ortygia, the historic city centre of Syracuse (in south-eastern Sicily). Specifically, the following carbonate stones have been investigated: 1) Syracuse limestone and 2) Melilli limestone, from the Monti Climiti Fm., 3) Oolitic limestone from the Monte Carrubba Fm., and 4) Giuggiulena limestone from the Pleistocene Panchina. All lithotypes underwent several mineralogical-petrographic and physical-mechanical investigations to individuate the causes responsible for their different durability when placed in the outdoor environment. Results obtained were also compared with literature data concerning the other two limestones employed as building and decorative materials in the façades of historic buildings in Ortygia, precisely the “Noto limestone” and the “Lumachelle limestone”, previously studied by other authors.
Results achieved are consistent with deterioration types macroscopically observed in the monuments, and highlight the close relationship between compositional, textural, physical and mechanical characteristics of the stone and its specific damage.
Black crusts are recognized to have been, up to now, one of the major deterioration forms affecting the built heritage in urban areas. Their formation is demonstrated to occur mainly on carbonate ...building materials, whose interaction with an SO
2
-loaded atmosphere leads to the transformation of calcium carbonate (calcite) into calcium sulfate dihydrate (gypsum) which, together with embedded carbonaceous particles, consequently forms the black crusts on the stone surface. An analytical study was carried out on black crust samples collected from limestone monumental buildings and churches belonging to the European built Heritage, i.e., the Corner Palace in Venice (Italy), the Cathedral of St. Rombouts in Mechelen (Belgium), and the Church of St. Eustache in Paris (France). For a complete characterization of the black crusts, an approach integrating different and complementary techniques was used, including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), Fourier transform infrared spectroscopy, optical and scanning electron microscopy. In particular, the application of LA-ICP-MS permitted to obtain a complete geochemical characterization in terms of trace elements of the black crusts from the inner parts to the external layers contributing to the identification of the major combustion sources responsible for the deterioration over time of the monuments under study. In addition, the obtained results revealed a relation between the height of sampling and the concentration of heavy metals and proved that the crust composition can be a marker to evaluate the variation of the fuels used over time.
The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in the Crab Nebula lasting for approximately nine days in April of 2011. The source, which at optical wavelengths has ...a size of approx =11 lt-yr across, doubled its gamma-ray flux within eight hours. The peak photon flux was (186 + or - 6) x 10 super(-7) cm super(-2) s super(-1) above 100 MeV, which corresponds to a 30-fold increase compared to the average value. During the flare, a new component emerged in the spectral energy distribution, which peaked at an energy of (375 + or - 26) MeV at flare maximum. The observations imply that the emission region was likely relativistically beamed toward us and that variations in its motion are responsible for the observed spectral variability.
•A field exposure test in two different urban environments is proposed.•The effect of urban air pollution on three different stones was assessed.•Physical features of stones affect the susceptibility ...to capture particulate.•Trace element concentrations provide information about pollution sources.
During the last decades, many studies have been carried out on environmental monitoring in specific sites aiming at their protection and conservation; however, researches focused on the direct implications, in terms of quantitative evaluation of stone deterioration, of these monitoring actions are still scarce.
This experimental work aims at monitoring the degradation processes affecting historical buildings constituted by carbonate stones. Specifically, specimens of Carrara marble and two limestones largely used in the Sicilian Baroque architecture, namely Noto and Comiso stones, were exposed outdoor in two Italian sites (Catania and Palermo), which are characterized by different environmental conditions. The field exposure test lasted two years. Both the substrates and the deposited particulate collected at the end of the exposure underwent several analytical investigations including: i) optical microscopy, mercury intrusion porosimetry, colorimetric analysis and roughness analysis, for the characterization of stone substrates before exposure; ii) ion chromatography (IC), infrared spectroscopy analysis (FT-IR) and inductively coupled plasma mass spectrometry (ICP-MS), for the characterization of the particulate deposited on stone surfaces. The obtained results highlighted blackening and yellowing processes of the carbonate substrates, chiefly on those specimens exposed in Palermo where such processes were more noticeable. Furthermore, the high concentration of sulphates and heavy metals detected (mainly in Palermo site) pointed out that both cities are mainly interested by mobile emission sources such as vehicular traffic. Additionally, analyses demonstrated the key-role of intrinsic features of the lithotypes in the degradation processes. In this regard, the higher porosity and surface roughness of Noto stone explains the major deposition of particulate with respect to the other two examined carbonate rocks.
This work belongs to the framework of the national research project “COMAS” (Planned COnservation, “
in situ
”, of underwater archaeological artifacts), funded by the Italian Ministry of Education, ...Universities and Research (MIUR), concerning the submarine archaeological area of Baia (Naples, Italy). The site includes remains of the ancient cities of
Baiae
and
Portus Iulius
, which, since the 4th century AD, started to be submerged because of the bradyseism phenomenon.
The work aims to the characterization of four different types of stone materials collected from the site, specifically marbles, limestones, ignimbrites, and bricks, in order to investigate their state of conservation. In particular, specimens were sampled from some masonry structures and pavement slabs (
opus sectile
) in a specific area of the submerged site, called “
Villa a Protiro
”.
In order to characterize archaeological samples from a mineralogical-petrographic point of view, polarized optical microscopy and X-ray diffraction analyses were carried out, while to assess their conservation state, the surface colonization by biodeteriogen agents and their interaction with the substrate were studied through observations under a stereomicroscope, scanning electron microscopy and Fourier transform infrared spectroscopy.
Marble and limestone samples revealed an intense bioerosion phenomena, attributable to epilithic and endolithic forms, particularly boring sponges. On the contrary, ignimbrites suffer a lower degree of biological colonization related to the activity of other species, such as serpulids and bryozoans. In bricks, biocolonisation is correlated to the type of temper used in the artifact, the quartz pastes having a greater susceptibility to biological attack than the volcanic ones.
This contribution focuses on the study of historical mortars from a Roman archaeological site known as Villa dei Quintili, a monumental villa located in the south‐eastern part of Rome (Italy). The ...study was carried out on 38 mortar samples, collected from several edifices within the complex. A multi‐analytical approach, including polarized optical microscopy, scanning electron microscopy coupled with energy‐dispersive system and laser ablation inductively coupled plasma mass spectrometry, was used to analyse the pozzolanic material used for the preparation of mortars. Data obtained on both major and trace elements were compared with the compositions of Pozzolana Rossa, Pozzolana Nera and Pozzolanella samples from the Alban Hills volcanic district, collected from a historic quarry nearby, as well as with literature data. The results of such a multidisciplinary approach allowed us to recognize the use of all three pozzolan types for the aggregate fraction of examined mortars from the Villa dei Quintili.
ABSTRACT
Galactic outflows are known to consist of several gas phases; however, the connection between these phases has been investigated little and only in a few objects. In this paper, we analyse ...Multi Unit Spectroscopic Explorer (MUSE)/Very Large Telescope (VLT) data of 26 local (U)LIRGs and study their ionized and neutral atomic phases. We also include objects from the literature to obtain a sample of 31 galaxies with spatially resolved multiphase outflow information. We find that the ionized phase of the outflows has on average an electron density three times higher than the disc (ne,disc ∼ 145 cm−3 versus ne,outflow ∼ 500 cm−3), suggesting that cloud compression in the outflow is more important than cloud dissipation. We find that the difference in extinction between outflow and disc correlates with the outflow gas mass. Together with the analysis of the outflow velocities, this suggests that at least some of the outflows are associated with the ejection of dusty clouds from the disc. This may support models where radiation pressure on dust contributes to driving galactic outflows. The presence of dust in outflows is relevant for potential formation of molecules inside them. We combine our data with millimetre data to investigate the molecular phase. We find that the molecular phase accounts for more than 60 ${{\ \rm per\ cent}}$ of the total mass outflow rate in most objects and this fraction is higher in active galactic nuclei (AGN)-dominated systems. The neutral atomic phase contributes of the order of 10 ${{\ \rm per\ cent}}$, while the ionized phase is negligible. The ionized-to-molecular mass outflow rate declines slightly with AGN luminosity, although with a large scatter.
Context.
Stellar feedback is one of the fundamental factors regulating the evolution of galaxies. However, we still do not have access to strong observational constraints on the relative importance ...of the different feedback mechanisms (e.g. radiation, ionised gas pressure, stellar winds) in driving H
II
region evolution and molecular cloud disruption. To quantify and compare the different feedback mechanisms, the size of an H
II
region is crucial, whereas samples of well-resolved H
II
regions are scarce.
Aims.
We constrain the relative importance of the various feedback mechanisms from young massive star populations by resolving H
II
regions across the disk of the nearby star-forming galaxy NGC 1672.
Methods.
We combined measurements of ionised gas nebular lines obtained by PHANGS-MUSE, with high-resolution (PSF
FWHM
∼ 0.1″; ∼10 pc) imaging from
Hubble
Space Telescope (HST) in both the narrow-band H
α
and broad-band (NUV,
U
,
B
,
V
,
I
) filters. We identified a sample of 40 isolated, compact H
II
regions in the HST H
α
image. We measured the sizes of these H
II
regions, which were previously unresolved in seeing-limited ground-based observations. In addition, we identified the ionisation source(s) for each H
II
region from catalogues produced as part of the PHANGS-HST survey. In doing so, we were able to link young stellar populations with the properties of their surrounding H
II
regions.
Results.
The HST observations allowed us to resolve all 40 regions, with radii between 5 and 40 pc. The H
II
regions investigated here are mildly dominated by thermal or wind pressure, yet their elevation above the radiation pressure is within the expected uncertainty range. We see that radiation pressure provides a substantially higher contribution to the total pressure than previously found in the literature over similar size scales. In general, we find higher pressures within more compact H
II
regions, which is driven by the inherent size scaling relations of each pressure term, albeit with significant scatter introduced by the variation in the stellar population properties (e.g. luminosity, mass, age, metallicity).
Conclusions.
For nearby galaxies, the combination of MUSE/VLT observations with stellar population and resolved H
α
observations from HST provides a promising approach that could yield the statistics required to map out how the importance of different stellar feedback mechanisms evolve over the lifetime of a H
II
region.
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