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  1. ABSTRACT The discovery of giant quasar Ly α nebulae at z > 2 has opened up the possibility to directly study in emission the Circumgalactic and Intergalactic Medium (CGM/IGM). However, the resonant nature of the Ly α line and its different emission mechanisms hamper the ability to constrain both the kinematics and physical properties of the CGM/IGM. Here, we present results of a pilot project aiming at the detection of CGM H α emission, a line which does not suffer from these limitations. To this end, we first used KCWI to detect Ly α emission around three bright quasars with 2.25 < z < 2.27, a range which is free from bright IR sky lines for H α, and then selected the most extended nebula for H α follow-up with MOSFIRE. Within the MOSFIRE slit, we detected H α emission extending up to 20 physical kpc with a total H α flux of FH α = (9.5 ± 0.9) × 10$^{-18}~\mathrm{erg\, s^{-1}\, cm^{-2}}$. Considering the Ly α flux in the same region, we found FLy α/FH α = 3.7 ± 0.3 consistent with that obtained for the Slug Nebula at z = 2.275 and with recombination radiation. This implies high densities or a very broad density distribution within the CGM of high-redshift quasars. Moreover, the H α line profile suggests the presence of multiple emitting components overlapping along our line of sight and relatively quiescent kinematics, which seems incompatible with either quasar outflows capable of escaping the potential well of the host halo or disc-like rotation in a massive halo (>1012 M⊙). 
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  2. Abstract

    This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshiftz≈ 0.4–1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small aslcl∼ 1 pc and density lower thannH= 10−3cm−3are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperatureTand the nonthermal motionsbNT, independent of the ionization models. On average,bNTis found to increase withlclfollowingbNTlcl0.3over three decades in spatial scale fromlcl≈ 1 pc tolcl≈ 1 kpc. Attributing the observedbNTto turbulent motions internal to the clumps, the best-fitbNTlclrelation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass ofϵ≈ 0.003 cm2s−3and a dissipation timescale of ≲100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferredϵis comparable to what is found in Civabsorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

     
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  3. ABSTRACT

    This paper presents a newly established sample of 19 unique galaxies and galaxy groups at redshift z = 0.89–1.21 in six QSO fields from the Cosmic Ultraviolet Baryon Survey (CUBS), designated as the CUBSz1 sample. In this sample, nine galaxies or galaxy groups show absorption features, while the other 10 systems exhibit 2σ upper limits of $\log N (\rm{He\,{\small I}})/\mbox{${\rm cm^{-2}}$}\lesssim 13.5$ and $\log N (\rm{O\,{\small V}})/\mbox{${\rm cm^{-2}}$}\lesssim 13.3$. Environmental properties of the galaxies, including galaxy overdensities, the total stellar mass and gravitational potential summed over all neighbours, and the presence of local ionizing sources, are found to have a significant impact on the observed CGM absorption properties. Specifically, massive galaxies and galaxies in overdense regions exhibit a higher rate of incidence of absorption. The CGM absorption properties in galaxy groups appear to be driven by the galaxy closest to the QSO sightline, rather than by the most massive galaxy or by mass-weighted properties. We introduce a total projected gravitational potential ψ, defined as −ψ/G = ∑Mhalo/dproj summed over all group members, to characterize the galaxy environment. This projected gravitational potential correlates linearly with the maximum density detected in each sightline (i.e. a power-law slope of $0.95_{-0.14}^{+0.15}$), consistent with higher pressure gas being confined in deeper gravitational potential wells. In addition, we find that the radial profile of cool gas density exhibits a decline from the inner regions to the outskirts, and the amplitude is consistent with the cool gas being in pressure balance with the hot halo. Finally, we note that the ionizing flux from nearby galaxies can elevate the N(H i)/N(He i) ratio, which provides a unique diagnostic of possible local sources contributing to the ionizing radiation field.

     
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  4. Seagroves, Scott ; Barnes, Austin ; Metevier, Anne ; Porter, Jason ; Hunter, Lisa (Ed.)
    I describe the design and implementation of a series of university MSc courses in Switzerland and in Italy on the topic of “Cosmic Structure Formation” whose goal has been to provide to the students a formative experience using interwoven research practice and fundamental scientific content. The course educational framework, which is based on the ISEE Inquiry Framework, emphasizes science, as much in teaching as in research, as a set of practices, re-discovering and actualizing in modern terms the original pivotal role which these practices had in education in ancient times. In particular, the courses focus on formative, intuitive, student-centered and dialogic learning in opposition to the informative, mnemonic, teacher-centered and monologic teaching of frontal lecture-based instruction, which is still the dominant teaching framework in university education, at least in Europe. I describe how course activities are designed in such a way as to mirror authentic research, including all aspects which are usually not practiced in lecture-based courses and “standard” laboratories (e.g., generating and refining questions; making and testing assumptions; developing one’s own research path; and sharing, explaining and justifying ideas and results with peers). Finally, I discuss the major outcomes of the courses and the main challenges which were faced in order to provide to the students a truly transformative experience which could allow them to improve both as learners and future scientific researchers, as well as members of a larger community. 
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  5. ABSTRACT

    We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous quasi-stellar objects (QSOs) at z ≈ 0.5–1.1. Spatially extended nebulae of ≈50–100 physical kpc in diameter centred on the QSOs are revealed in [O ii] $\lambda \lambda \, 3727,3729$ and/or [O iii] $\lambda \, 5008$ emission lines in integral field spectroscopic observations obtained using Multi-Unit Spectroscopic Explorer on the Very Large Telescope. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from ≲5 kpc to ≈20–50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of ≈0.2 cm2 s−3. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium.

     
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  6. ABSTRACT

    This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift z ≲ 1. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from $\log (n_{\rm H}/{{\rm cm^{-3}}}) \approx -4$ to −1, while the temperature of the gas is confined in a narrow range of log (T/K) ≈ 4.3 ± 0.3. In addition, a weak anticorrelation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30 per cent of the components at z ≲ 1 exhibit line widths driven by non-thermal motions, in comparison to <20 per cent found at z ≈ 2–3. Attributing the observed non-thermal line widths to intra-clump turbulence, we find that massive quenched galaxies on average exhibit higher non-thermal broadening/turbulent energy in their CGM compared to star-forming galaxies at z ≲ 1. Finally, strong absorption features from multiple ions covering a wide range of ionization energy (e.g. from Mg ii to O iv) can be present simultaneously in a single absorption system with kinematically aligned component structure, but the inferred pressure in different phases may differ by a factor of ≈10.

     
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  7. ABSTRACT We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $N_\mathrm{H\, I}\approx (1-3)\times 10^{16}\, \mathrm{cm}^{-2}$ discovered at $z$ = 0.5 in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multiphase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred α-element abundance varying from [α/H] ≈−0.8 to near solar and densities spanning over two decades from log nH/cm−3 ≈ −2.2 to <−4.3. Available deep galaxy survey data from the CUBS program taken with VLT/MUSE, Magellan/LDSS3-C and Magellan/IMACS reveal that the $z$ = 0.47 system is located 55 kpc from a star-forming galaxy with prominent Balmer absorption of stellar mass ${{M_{\rm star}}}\approx 2\times 10^{10}\, {{M_{\odot}}}$, while the $z$ = 0.54 system resides in an overdense environment of 11 galaxies within 750 kpc in projected distance, with the most massive being a luminous red galaxy of ${{M_{\rm star}}}\approx 2\times 10^{11}\, {{M_{\odot}}}$ at 375 kpc. The study of these two pLLSs adds to an emerging picture of the complex, multiphase circumgalactic gas that varies in chemical abundances and density on small spatial scales in diverse galaxy environments. The inhomogeneous nature of metal enrichment and density revealed in observations must be taken into account in theoretical models of diffuse halo gas. 
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  8. null (Ed.)
    ABSTRACT We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at z = 0.36–0.6 discovered within the cosmic ultraviolet baryon survey (CUBS). Because intervening LLSs at z < 1 suppress far-UV (ultraviolet) light from background QSOs, an unbiased search of these absorbers requires a near-UV-selected QSO sample, as achieved by CUBS. CUBS LLSs exhibit multicomponent kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states such as C ii, C iii, N iii, Mg ii, Si ii, Si iii, O ii, O iii, O vi, and Fe ii absorption that span several hundred km s−1 in line-of-sight velocity. Specifically, higher column density components (log N(H i)/cm−2≳ 16) in all four absorbers comprise dynamically cool gas with $\langle T \rangle =(2\pm 1) \times 10^4\,$K and modest non-thermal broadening of $\langle b_\mathrm{nt} \rangle =5\pm 3\,$km s−1. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modelling that takes into account the resolved component structures of H i and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $160^{+140}_{-50}$ pc. While obtaining robust metallicity constraints for the low density, highly ionized phase remains challenging due to the uncertain $N\mathrm{(H\, {\small I})}$, we demonstrate that the cool-phase gas in LLSs has a median metallicity of $\mathrm{[\alpha /H]_{1/2}}=-0.7^{+0.1}_{-0.2}$, with a 16–84 percentile range of [α/H] = (−1.3, −0.1). Furthermore, the wide range of inferred elemental abundance ratios ([C/α], [N/α], and [Fe/α]) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the z < 1 circumgalactic medium. 
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  9. Abstract

    We present the discovery of neutral gas detected in both damped Lyαabsorption (DLA) and Hi21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an Hibridge connecting two interacting dwarf galaxies (log (Mstar/M) = 8.5 ± 0.2) that host az= 0.026 DLA with log[N(Hi)/cm−2] = 20.60 ± 0.05 toward the QSO J2339−5523 (zQSO= 1.35). At impact parameters ofd= 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L*within at least Δv= ±300 km s−1andd≈ 350 kpc. The Hi21 cm emission is spatially coincident with the DLA at the 2σ–3σlevel per spectral channel over several adjacent beams. However, Hi21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratioTs/fc> 1880 K). Observations with VLT-MUSE demonstrate that theα-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and Hi21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

     
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