Abstract
We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in ...the context of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry–Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favors active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly accreting neutron star within an evolved stellar population region.
ABSTRACT
Follow-up observations of (sub-)mm-selected gravitationally lensed systems have allowed a more detailed study of the dust-enshrouded phase of star formation up to very early cosmic times. ...Here, the case of the gravitationally lensed merger in HATLAS J142935.3–002836 (also known as H1429−0028; zlens = 0.218, zbkg = 1.027) is revisited following recent developments in the literature and new Atacama Pathfinder EXperiment (APEX) observations targeting two carbon monoxide (CO) rotational transitions Jup = 3 and 6. We show that the line profiles comprise three distinct velocity components, where the fainter high velocity one is less magnified and more compact. The modelling of the observed spectral line energy distribution of CO Jup = 2–6 and C i 3P1−3P0 assumes a large velocity gradient scenario, where the analysis is based on four statistical approaches. Since the detected gas and dust emission comes exclusively from only one of the two merging components (the one oriented north–south, NS), we are only able to determine upper limits for the companion. The molecular gas in the NS component in H1429−0028 is found to have a temperature of ∼70 K, a volume density of log (ncm−3) ∼ 3.7, to be expanding at ∼10 km s−1 pc−1, and amounts to ${M_{\rm H_2} = 4_{-2}^{+3} \times 10^9\,{\rm M}_\odot }$. The CO to H2 conversion factor is estimated to be $\alpha _{\rm CO} = 0.4_{-0.2}^{+0.3}\,$ M⊙/(K km s−1 pc2). The NS galaxy is expected to have a factor of ≳10× more gas than its companion (${M_{\rm H_2}}\lesssim 3\times 10^8$ M⊙). Nevertheless, the total amount of molecular gas in the system comprises only up to 15 per cent (1σ upper limit) of the total (dynamical) mass.
The two SCUBA HAlf-Degree Extragalactic Survey (SHADES) fields are amongst the richest places in the sky in terms of multi-wavelength coverage. They comprise an eastern section of the Lockman Hole ...(LH) and the central portion of the Subaru- XMM/Newton Deep Field (SXDF). In this thesis, I have obtained extremely deep, multi-frequency radio imaging of the SHADES fields using the GiantMetre-wave Radio Telescope (GMRT) and the Very Large Array (VLA), at 610MHz and 1.4GHz, respectively. These data are used to analyse the nature of the sub-milliJansky (sub-mJy) radio population, which has been hotly debated in the last few years: are they powered by star-forming or nuclear activity? To tackle the problem, I employ different approaches making use of the large variety of multi-wavelength data in the SHADES fields. I begin by analysing the spectral index, α610MHz 1.4GHz , of radio sources detected in the LH, to explore the dominant emission mechanism. Based on a robust 10 σ detection criterion, I find a constantmedian spectral index of α610MHz 1.4GHz ≈ −0.6 to −0.7 for sources between S1.4GHz ≈ 200 μJy and 10mJy. This result suggests that the galaxy population in the sub-mJy regime is powered by optically-thin synchrotron emission – starforming galaxies or lobe-dominated active galactic nuclei (AGN). Making use of X-ray observations in the LH, I show that the fraction of radio sources detected in the hard X-ray band (between 2 and 10 keV) decreases from 50 to 15 per cent between S1.4GHz ≈ 1mJy and . 100 μJy, which strongly suggests a transition from AGN to star-forming galaxies. Based on the deep, multi-wavelength coverage of the SXDF, I explore the behaviour of the far-infrared (FIR)/radio correlation as a function of redshift. I combine the q24 factor – the logarithmic flux density ratio between Spitzer 24-μm and VLA 1.4- GHz flux densities – with available photometric redshifts and find strong evidence that the correlation holds out to z ≈ 3.5. Based on M82-like k-corrections and using a high-significance (S1.4GHz > 300 μJy) radio sub-sample, I find a mean and scatter of q24 = 0.71 ± 0.47. Monte-Carlo simulations based on these findings show that fewer sources deviate from the correlation at fainter flux densities (i.e. fewer radioloud AGN). I predict that the radio-loud fraction drops from 50 per cent at ∼ 1mJy to zero at . 100 μJy. The validity of the FIR/radio correlation out to very high redshifts adds credibility to identifications of sub-millimetre (submm) galaxies (SMGs) made at radio wavelengths. Based on a sample of 45 radio-identified SMGs in the LH, I find a median radio spectral index of α610MHz 1.4GHz = −0.72 ± 0.07, which suggests that optically-thin synchrotron is the dominant radio emission mechanism. Finally, as anAppendix I include a theoretical treatment that constrains the average geometry of the dusty, torus-like structures believed to obscure a large fraction of the AGN population. I use the distribution of column densities (NH) obtained from deep ∼ 1Msec X-ray observations in the Chandra Deep Field South. I find that to reproduce the wide observed range of NH, the best torus model is given by a classical “donut”- shaped distribution with an exponential angular dependency of the density profile.
The two SCUBA HAlf-Degree Extragalactic Survey (SHADES) fields are amongst the richest places in the sky in terms of multi-wavelength coverage. They comprise an eastern section of the Lockman Hole ...(LH) and the central portion of the Subaru- XMM/Newton Deep Field (SXDF). In this thesis, I have obtained extremely deep, multi-frequency radio imaging of the SHADES fields using the GiantMetre-wave Radio Telescope (GMRT) and the Very Large Array (VLA), at 610MHz and 1.4GHz, respectively. These data are used to analyse the nature of the sub-milliJansky (sub-mJy) radio population, which has been hotly debated in the last few years: are they powered by star-forming or nuclear activity? To tackle the problem, I employ different approaches making use of the large variety of multi-wavelength data in the SHADES fields. I begin by analysing the spectral index, α610MHz 1.4GHz , of radio sources detected in the LH, to explore the dominant emission mechanism. Based on a robust 10 σ detection criterion, I find a constantmedian spectral index of α610MHz 1.4GHz ≈ −0.6 to −0.7 for sources between S1.4GHz ≈ 200 μJy and 10mJy. This result suggests that the galaxy population in the sub-mJy regime is powered by optically-thin synchrotron emission – starforming galaxies or lobe-dominated active galactic nuclei (AGN). Making use of X-ray observations in the LH, I show that the fraction of radio sources detected in the hard X-ray band (between 2 and 10 keV) decreases from 50 to 15 per cent between S1.4GHz ≈ 1mJy and . 100 μJy, which strongly suggests a transition from AGN to star-forming galaxies. Based on the deep, multi-wavelength coverage of the SXDF, I explore the behaviour of the far-infrared (FIR)/radio correlation as a function of redshift. I combine the q24 factor – the logarithmic flux density ratio between Spitzer 24-μm and VLA 1.4- GHz flux densities – with available photometric redshifts and find strong evidence that the correlation holds out to z ≈ 3.5. Based on M82-like k-corrections and using a high-significance (S1.4GHz > 300 μJy) radio sub-sample, I find a mean and scatter of q24 = 0.71 ± 0.47. Monte-Carlo simulations based on these findings show that fewer sources deviate from the correlation at fainter flux densities (i.e. fewer radioloud AGN). I predict that the radio-loud fraction drops from 50 per cent at ∼ 1mJy to zero at . 100 μJy. The validity of the FIR/radio correlation out to very high redshifts adds credibility to identifications of sub-millimetre (submm) galaxies (SMGs) made at radio wavelengths. Based on a sample of 45 radio-identified SMGs in the LH, I find a median radio spectral index of α610MHz 1.4GHz = −0.72 ± 0.07, which suggests that optically-thin synchrotron is the dominant radio emission mechanism. Finally, as anAppendix I include a theoretical treatment that constrains the average geometry of the dusty, torus-like structures believed to obscure a large fraction of the AGN population. I use the distribution of column densities (NH) obtained from deep ∼ 1Msec X-ray observations in the Chandra Deep Field South. I find that to reproduce the wide observed range of NH, the best torus model is given by a classical “donut”- shaped distribution with an exponential angular dependency of the density profile.
A&A 654, A128 (2021) We characterize the ionized gas outflows in 15 low-redshift star-forming
galaxies, a Valpara\'iso ALMA Line Emission Survey (VALES) subsample, using
MUSE integral field ...spectroscopy and GAMA photometric broadband data. We
measure the emission-line spectra by fitting a double-component profile, with
the second and broader component being related to the outflowing gas. This
interpretation is in agreement with the correlation between the observed
star-formation rate surface density ($\Sigma_{\mathrm{SFR}}$) and the
second-component velocity dispersion ($\sigma_{\mathrm{2nd}}$), expected when
tracing the feedback component. By modelling the broadband spectra with spectra
energy distribution (SED) fitting and obtaining the star-formation histories of
the sample, we observe a small decrease in SFR between 100 and 10 Myr in
galaxies when the outflow H$\alpha$ luminosity contribution is increased,
indicating that the feedback somewhat inhibits the star formation within these
timescales. The observed emission-line ratios are best reproduced by
photoionization models when compared to shock-ionization, indicating that
radiation from young stellar population is dominant, and seems to be a
consequence of a continuous star-formation activity instead of a bursty event.
The outflow properties such as mass outflow rate ($\sim 0.1\,$M$_\odot$
yr$^{-1}$), outflow kinetic power ($\sim 5.2 \times 10^{-4}\%
L_{\mathrm{bol}}$) and mass loading factor ($\sim 0.12$) point towards a
scenario where the measured feedback is not strong and has a low impact on the
evolution of galaxies in general.
Galaxy morphology is shaped by stellar activity, feedback, gas and dust
properties, and interactions with surroundings, and can therefore provide
insight into these processes. In this paper, we study ...the spatial offsets
between stellar and interstellar medium emission in a sample of 54
main-sequence star-forming galaxies at $z\sim4-6$ observed with the Atacama
Large Millimeter/submillimeter Array (ALMA) and drawn from the ALMA Large
Program to INvestigate C$^+$ at Early times (ALPINE). We find no significant
spatial offset for the majority ($\sim$ 70 percent) of galaxies in the sample
among any combination of C II, far-infrared continuum, optical, and
ultraviolet emission. However, a fraction of the sample ($\sim$ 30 percent)
shows offsets larger than the median by more than 3$\sigma$ significance
(compared to the uncertainty on the offsets), especially between C II and
ultraviolet emission. We find that these significant offsets are of the order
of $\sim$0.5-0.7 arcsec, corresponding to $\sim$3.5-4.5 kiloparsecs. The
offsets could be caused by a complex dust geometry, strong feedback from stars
and active galactic nuclei, large-scale gas inflow and outflow, or a
combination of these phenomena. However, our current analysis does not
definitively constrain the origin. Future, higher resolution ALMA and JWST
observations may help resolve the ambiguity. Regardless, since there exist at
least some galaxies that display such large offsets, galaxy models and spectral
energy distribution fitting codes cannot assume co-spatial emission in all
main-sequence galaxies, and must take into account that the observed emission
across wavelengths may be spatially segregated.
We present the radio properties of 66 spectroscopically-confirmed normal
star-forming galaxies (SFGs) at $4.4<z<5.9$ in the COSMOS field that were C
II detected in the Atacama Large Millimeter Array ...(ALMA) Large Program to
INvestigate C II at Early times (ALPINE). We separate these galaxies
("CII-detected-all") into lower redshift ("CII-detected-lz", $\langle
z\rangle=4.5$) and higher redshift ("CII-detected-hz", $\langle z\rangle=5.6$)
sub-samples and stack multi-wavelength imaging for each sub-sample from X-ray
to radio bands. A radio signal is detected in the stacked 3 GHz image of
CII-detected-all and -lz samples at $\gtrsim3\sigma$. We find that the
infrared-radio correlation of our sample, quantified by $q_{\mathrm{TIR}}$, is
lower than the local relation for normal SFGs at $\sim$3$\sigma$ significance
level, and is instead broadly consistent with that of bright sub-mm galaxies at
$2<z<5$. Neither of these samples show evidence of dominant AGN activity in
their stacked Spectral Energy Distributions (SEDs), rest-frame UV spectra, or
X-ray images. Although we cannot rule out the possible effect of the assumed
spectral index and the applied infrared SED templates as at least partially
causing these differences, the lower obscured fraction of star formation than
at lower redshift can alleviate the tension between our stacked
$q_{\mathrm{TIR}}$s and that of local normal SFGs. It is possible that the dust
buildup, which primarily governs the IR emission in addition to older stellar
populations, has not had enough time to occur fully in these galaxies, whereas
the radio emission can respond on a more rapid timescale. Therefore, we might
expect a lower $q_{\mathrm{TIR}}$ to be a general property of high-redshift
SFGs.
We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in the context ...of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry-Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favours active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly-accreting neutron star within an evolved stellar population region.
Follow-up observations of (sub-)mm-selected gravitationally-lensed systems have allowed a more detailed study of the dust-enshrouded phase of star-formation up to very early cosmic times. Here, the ...case of the gravitationally lensed merger in HATLAS J142935.3-002836 (also known as H1429-0028; z_lens=0.218, z_bkg=1.027) is revisited following recent developments in the literature and new APEX observations targeting two carbon monoxide (CO) rotational transitions J_up=3 and 6. We show that the line-profiles comprise three distinct velocity components, where the fainter high-velocity one is less magnified and more compact. The modelling of the observed spectral line energy distribution of CO J_up=2 to 6 and CI3P_1-3P_0 assumes a large velocity gradient scenario, where the analysis is based on four statistical approaches. Since the detected gas and dust emission comes exclusively from only one of the two merging components (the one oriented North-South, NS), we are only able to determine upper-limits for the companion. The molecular gas in the NS component in H1429-0028 is found to have a temperature of ~70K, a volume density of log(n/cm3)~3.7, to be expanding at ~10km/s/pc, and amounts to M_H2=4(-2,+3)*1e9 Msun. The CO to H2 conversion factor is estimated to be alpha_CO=0.4(-0.2,+0.3) Msun/(K.km/s.pc2). The NS galaxy is expected to have a factor of >10x more gas than its companion (M_H2<3e8 Msun). Nevertheless, the total amount of molecular gas in the system comprises only up to 15 per cent (1sigma upper-limit) of the total (dynamical) mass.
Galaxy morphology is shaped by stellar activity, feedback, gas and dust properties, and interactions with surroundings, and can therefore provide insight into these processes. In this paper, we study ...the spatial offsets between stellar and interstellar medium emission in a sample of 54 main-sequence star-forming galaxies at \(z\sim4-6\) observed with the Atacama Large Millimeter/submillimeter Array (ALMA) and drawn from the ALMA Large Program to INvestigate C\(^+\) at Early times (ALPINE). We find no significant spatial offset for the majority (\(\sim\) 70 percent) of galaxies in the sample among any combination of C II, far-infrared continuum, optical, and ultraviolet emission. However, a fraction of the sample (\(\sim\) 30 percent) shows offsets larger than the median by more than 3\(\sigma\) significance (compared to the uncertainty on the offsets), especially between C II and ultraviolet emission. We find that these significant offsets are of the order of \(\sim\)0.5-0.7 arcsec, corresponding to \(\sim\)3.5-4.5 kiloparsecs. The offsets could be caused by a complex dust geometry, strong feedback from stars and active galactic nuclei, large-scale gas inflow and outflow, or a combination of these phenomena. However, our current analysis does not definitively constrain the origin. Future, higher resolution ALMA and JWST observations may help resolve the ambiguity. Regardless, since there exist at least some galaxies that display such large offsets, galaxy models and spectral energy distribution fitting codes cannot assume co-spatial emission in all main-sequence galaxies, and must take into account that the observed emission across wavelengths may be spatially segregated.
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