arXiv subjects

Riccardo Pavesi

Publications and source records attributed to Riccardo Pavesi.

17 recordsLinked to original sources

arXiv2021

Molecular Gas Excitation of the Massive Dusty Starburst CRLE and the Main-Sequence Galaxy HZ10 at z=5.7 in the COSMOS Field

We report CO(5$\rightarrow$4) and CO(6$\rightarrow$5) line observations in the dusty starbursting galaxy CRLE ($z = 5.667$) and the main-sequence (MS) galaxy HZ10 ($z = 5.654$) with the Northern Extended Millimeter Array (NOEMA). CRLE is the most luminous $z>5$ starburst in the COSMOS field and HZ10 is the most gas-rich "normal" galaxy currently known at $z>5$. We find line luminosities for CO(5$\rightarrow$4) and CO(6$\rightarrow$5) of (4.9 $\pm$ 0.5) and (3.8 $\pm$ 0.4) $\times$ 10$^{10}$ K km s$^{-1}$ pc$^{2}$ for CRLE and upper limits of $< 0.76$ and $< 0.60$ $\times$ 10$^{10}$ K km s$^{-1}$ pc$^{2}$ for HZ10, respectively. The CO excitation of CRLE appears comparable to other $z>5$ dusty star-forming galaxies (DSFGs). For HZ10, these line luminosity limits provide the first significant constraints of this kind for a MS galaxy at $z > 5$. We find the upper limit of $L'_{5\rightarrow4}/L'_{2\rightarrow1}$ in HZ10 could be similar to the average value for MS galaxies around $z\approx 1.5$, suggesting that MS galaxies with comparable gas excitation may already have existed one billion years after the Big Bang. For CRLE we determine the most likely values for the H$_2$ density, kinetic temperature and dust temperature based on excitation modeling of the CO line ladder. We also derive a total gas mass of $(7.1 \pm 1.3) \times 10^{10} M_\odot$. Our findings provide some of the currently most detailed constraints on the gas excitation that sets the conditions for star formation in a galaxy protocluster environment at $z > 5$.

astro-ph.GA↗

arXiv2021

COLDz: Probing Cosmic Star Formation With Radio Free-free Emission

Radio free-free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum -- being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys -- the usage of free-free emission as a star formation rate tracer has mostly remained limited to the local Universe. Here we perform a multi-frequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10 and 34 GHz in the COSMOS and GOODS-North fields to probe free-free emission in typical galaxies at the peak of cosmic star formation. We find that $z \sim 0.5 - 3$ star-forming galaxies exhibit radio emission at rest-frame frequencies of $\sim 65 - 90$ GHz that is $\sim 1.5 - 2\times$ fainter than would be expected from a simple combination of free-free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free-free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free-free emission at $0.5 \lesssim z \lesssim 3$, which are in good agreement with more established tracers at high redshift. In the future, deep multi-frequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free-free emission as a tracer of high-redshift star formation.

astro-ph.GA↗

arXiv2020

ALMA Characterises the Dust Temperature of z ~ 5.5 Star-Forming Galaxies

The infrared spectral energy distributions (SEDs) of main-sequence galaxies in the early universe (z > 4) is currently unconstrained as infrared continuum observations are time consuming and not feasible for large samples. We present Atacama Large Millimetre Array (ALMA) Band 8 observations of four main-sequence galaxies at z ~ 5.5 to study their infrared SED shape in detail. Our continuum data (rest-frame 110$\rm μm$, close to the peak of infrared emission) allows us to constrain luminosity weighted dust temperatures and total infrared luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame 100$\rm μm$. The derived dust peak temperatures at z ~ 5.5 (38$\pm$8K) are elevated compared to average local galaxies, however, 5-10K below what would be predicted from an extrapolation of the trend at $z<4$. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the infrared SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the 850$\rm μm$ dust continuum, we derive molecular gas masses between $10^{10}$ and $10^{11}\,{\rm M_{\odot}}$ and gas fractions (gas over total mass) of 30-80% (gas depletion times of 100-220Myrs). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe.

astro-ph.GA↗

arXiv2020

COLDz: A High Space Density of Massive Dusty Starburst Galaxies ~1 Billion Years after the Big Bang

We report the detection of CO($J$=2$\to$1) emission from three massive dusty starburst galaxies at $z$$>$5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 ($z$=5.183) and AzTEC-3 ($z$=5.298), were previously known. We revise a previous redshift estimate for the third source GN10 ($z$=5.303), which we have independently confirmed through detections of CO $J$=1$\to$0, 5$\to$4, 6$\to$5, and [CII] 158 $μ$m emission with the VLA and the NOrthern Extended Milllimeter Array (NOEMA). We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at $z$$>$5. Given our survey area of $\sim$60 arcmin$^2$, our results appear to imply a $\sim$6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these $z$$>$5 galaxies show star-formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions - consistent with the more extended sizes of the [CII] emission compared to the dust continuum and higher [CII]-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between $z$$>$5 dusty starbursts, which typically have dust temperatures $\sim$57%$\pm$25% warmer than starbursts at $z$=2-3 due to their enhanced star formation activity.

astro-ph.GA↗

arXiv2019

Low star formation efficiency in typical galaxies at z=5-6

Using the VLA and ALMA, we have obtained CO(2-1), [C II], [N II] line emission and multiple dust continuum measurements in a sample of "normal" galaxies at $z=5-6$. We report the highest redshift detection of low-$J$ CO emission from a Lyman Break Galaxy, at $z\sim5.7$. The CO line luminosity implies a massive molecular gas reservoir of $(1.3\pm0.3)(α_{\rm CO}/4.5\,M_\odot$ (K km s$^{-1}$ pc$^2)^{-1})\times10^{11}\,M_\odot$, suggesting low star formation efficiency, with a gas depletion timescale of order $\sim$1 Gyr. This efficiency is much lower than traditionally observed in $z\gtrsim5$ starbursts, indicating that star forming conditions in Main Sequence galaxies at $z\sim6$ may be comparable to those of normal galaxies probed up to $z\sim3$ to-date, but with rising gas fractions across the entire redshift range. We also obtain a deep CO upper limit for a Main Sequence galaxy at $z\sim5.3$ with $\sim3$ times lower SFR, perhaps implying a high $α_{\rm CO}$ conversion factor, as typically found in low metallicity galaxies. For a sample including both CO targets, we also find faint [N II] 205$\,μ$m emission relative to [C II] in all but the most IR-luminous "normal" galaxies at $z=5-6$, implying more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties suggest that low metallicity may be common in typical $\sim$10$^{10}\,M_\odot$ galaxies at $z=5-6$. While a fraction of Main Sequence star formation in the first billion years may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.

astro-ph.GA↗

arXiv2019

The Molecular Gas Reservoirs of $z\sim 2$ Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses

We test the use of long-wavelength dust continuum emission as a molecular gas tracer at high redshift, via a unique sample of 12, z~2 galaxies with observations of both the dust continuum and CO(1-0) line emission (obtained with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array, respectively). Our work is motivated by recent, high redshift studies that measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration of the rest-frame $850μ$m luminosity ($L_\mathrm{850μm,rest}$) against the CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We hereby test whether this method is valid for the types of high-redshift, star-forming galaxies to which it has been applied. We recover a clear correlation between the rest-frame $850μ$m luminosity, inferred from the single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent with the samples used to perform the $850μ$m calibration. The molecular gas masses, derived from $L_\mathrm{850μm,rest}$, agree to within a factor of two with those derived from CO(1-0). We show that this factor of two uncertainty can arise from the values of the dust emissivity index and temperature that need to be assumed in order to extrapolate from the observed frequency to the rest-frame at 850$\mathrm{μm}$. The extrapolation to 850$\mathrm{μm}$ therefore has a smaller effect on the accuracy of \Mmol\ derived via single-band dust-continuum observations than the assumed CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore conclude that single-band observations of long-wavelength dust emission can be used to reliably constrain the molecular gas masses of massive, star-forming galaxies at $z\gtrsim2$.

astro-ph.GA↗

arXiv2019

The evolution of the cosmic molecular gas density

One of the last missing pieces in the puzzle of galaxy formation and evolution through cosmic history is a detailed picture of the role of the cold gas supply in the star-formation process. Cold gas is the fuel for star formation, and thus regulates the buildup of stellar mass, both through the amount of material present through a galaxy's gas mass fraction, and through the efficiency at which it is converted to stars. Over the last decade, important progress has been made in understanding the relative importance of these two factors along with the role of feedback, and the first measurements of the volume density of cold gas out to redshift 4, (the "cold gas history of the Universe") has been obtained. To match the precision of measurements of the star formation and black-hole accretion histories over the coming decades, a two orders of magnitude improvement in molecular line survey speeds is required compared to what is possible with current facilities. Possible pathways towards such large gains include significant upgrades to current facilities like ALMA by 2030 (and beyond), and eventually the construction of a new generation of radio-to-millimeter wavelength facilities, such as the next generation Very Large Array (ngVLA) concept.

astro-ph.GA↗

arXiv2019

High gas fraction in a CO-selected main-sequence galaxy at $z > 3$

We report NOrthern Extended Millimetre Array (NOEMA) observations of warm molecular gas traced by CO($5-4$) in a $z \sim 3.2$ gas-rich main-sequence galaxy (MS), initially serendipitously detected in CO($3-2$) emission in `blind' deep NOEMA observations. Our target shows a gas excitation consistent with that seen in $z \sim 1.5$ MS galaxies ($L'_{\rm CO( 5 - 4)}/L'_{\rm CO (3 - 2)} = 0.41 \pm 0.14$), albeit toward the low end, as well as a similar star formation efficiency based on the CO($3-2$) line luminosity and the $L_{\rm IR}$. However, it shows a high molecular gas fraction ($f_{\rm gas} = 0.9\pm 0.2$) as compared to $z\sim 1.5$ MS galaxies ($f_{\rm gas} \sim 0.4$), consistent with a cosmologically increasing gas fraction beyond $z\gtrsim3$ and our current understanding of scaling relations between $z$, $f_{\rm gas}$, the stellar mass $M_*$, and the specific star formation rate sSFR. Our results are consistent with recent findings by the COLDz and ASPECS molecular line scan surveys and suggest that deep searches for CO emission are a powerful means to identify gas-rich, star-forming galaxies at high redshift.

astro-ph.GA↗

arXiv2019

COLDz: Shape of the CO Luminosity Function at High Redshift and the Cold Gas History of the Universe

We report the first detailed measurement of the shape of the CO luminosity function at high redshift, based on $>$320 hr of the NSF's Karl G. Jansky Very Large Array (VLA) observations over an area of $\sim$60 arcmin$^2$ taken as part of the CO Luminosity Density at High Redshift (COLDz) survey. COLDz "blindly" selects galaxies based on their cold gas content through CO($J$=1$\to$0) emission at $z$$\sim$2-3 and CO($J$=2$\to$1) at $z$$\sim$5-7 down to a CO luminosity limit of log($L'_{\rm CO}$/K km s$^{-1}$ pc$^2$)$\simeq$9.5. We find that the characteristic luminosity and bright end of the CO luminosity function are substantially higher than predicted by semi-analytical models, but consistent with empirical estimates based on the infrared luminosity function at $z$$\sim$2. We also present the currently most reliable measurement of the cosmic density of cold gas in galaxies at early epochs, i.e., the cold gas history of the universe, as determined over a large cosmic volume of $\sim$375,000 Mpc$^3$. Our measurements are in agreement with an increase of the cold gas density from $z$$\sim$0 to $z$$\sim$2-3, followed by a possible decline towards $z$$\sim$5-7. These findings are consistent with recent surveys based on higher-$J$ CO line measurements, upon which COLDz improves in terms of statistical uncertainties by probing $\sim$50-100 times larger areas and in the reliability of total gas mass estimates by probing the low-$J$ CO lines accessible to the VLA. Our results thus appear to suggest that the cosmic star-formation rate density follows an increased cold molecular gas content in galaxies towards its peak about 10 billion years ago, and that its decline towards the earliest epochs is likely related to a lower overall amount of cold molecular gas (as traced by CO) bound in galaxies towards the first billion years after the Big Bang.

astro-ph.GA↗

arXiv2018

The CO Luminosity Density at High-z (COLDz) Survey: A Sensitive, Large Area Blind Search for Low-J CO Emission from Cold Gas in the Early Universe with the Karl G. Jansky Very Large Array

We describe the CO Luminosity Density at High-z (COLDz) survey, the first spectral line deep field targeting CO(1-0) emission from galaxies at $z=1.95-2.85$ and CO(2-1) at $z=4.91-6.70$. The main goal of COLDz is to constrain the cosmic density of molecular gas at the peak epoch of cosmic star formation. By targeting both a wide ($\sim$51 arcmin$^2$) and a deep area ($\sim$9 arcmin$^2$), the survey is designed to robustly constrain the bright end and the characteristic luminosity of the CO(1-0) luminosity function. An extensive analysis of the reliability of our line candidates, and new techniques provide detailed completeness and statistical corrections as necessary to determine the best constraints to date on the CO luminosity function. Our blind search for CO(1-0) uniformly selects starbursts and massive Main Sequence galaxies based on their cold molecular gas masses. Our search also detects CO(2-1) line emission from optically dark, dusty star-forming galaxies at $z>5$. We find a range of spatial sizes for the CO-traced gas reservoirs up to $\sim40$ kpc, suggesting that spatially extended cold molecular gas reservoirs may be common in massive, gas-rich galaxies at $z\sim2$. Through CO line stacking, we constrain the gas mass fraction in previously known typical star-forming galaxies at $z=2$-3. The stacked CO detection suggests lower molecular gas mass fractions than expected for massive Main Sequence galaxies by a factor of $\sim3-6$. We find total CO line brightness at $\sim34\,$GHz of $0.45\pm0.2\,μ$K, which constrains future line intensity mapping and CMB experiments.

astro-ph.GA↗

arXiv2018

Hidden in plain sight: a massive, dusty starburst in a galaxy protocluster at z=5.7 in the COSMOS field

We report the serendipitous discovery of a dusty, starbursting galaxy at $z=5.667$ (hereafter called CRLE) in close physical association with the "normal" main-sequence galaxy HZ10 at $z=5.654$. CRLE was identified by detection of [CII], [NII] and CO(2-1) line emission, making it the highest redshift, most luminous starburst in the COSMOS field. This massive, dusty galaxy appears to be forming stars at a rate of at least 1500$\,M_\odot$ yr$^{-1}$ in a compact region only $\sim3$ kpc in diameter. The dynamical and dust emission properties of CRLE suggest an ongoing merger driving the starburst, in a potentially intermediate stage relative to other known dusty galaxies at the same epoch. The ratio of [CII] to [NII] may suggest that an important ($\sim15\%$) contribution to the [CII] emission comes from a diffuse ionized gas component, which could be more extended than the dense, starbursting gas. CRLE appears to be located in a significant galaxy overdensity at the same redshift, potentially associated with a large-scale cosmic structure recently identified in a Lyman Alpha Emitter survey. This overdensity suggests that CRLE and HZ10 reside in a protocluster environment, offering the tantalizing opportunity to study the effect of a massive starburst on protocluster star formation. Our findings support the interpretation that a significant fraction of the earliest galaxy formation may occur from the inside out, within the central regions of the most massive halos, while rapidly evolving into the massive galaxy clusters observed in the local Universe.

astro-ph.GA↗

arXiv2017

Are high redshift Galaxies hot? - Temperature of z > 5 Galaxies and Implications on their Dust Properties

Recent studies have found a significant evolution and scatter in the IRX-$β$ relation at z > 4, suggesting different dust properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis but poorly constrained in normal (main-sequence) star-forming z > 5 galaxies where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogs of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) SED compared to average z < 4 galaxies that are used as prior in these studies. The blue-shifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of the metal-poor inter-stellar medium (ISM) being optically thin to ultra-violet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests 0.6 dex increased total FIR luminosities, which removes some tension between dust attenuation models and observations of the IRX-$β$ relation at z > 5. Despite this, some galaxies still fall below the minimum IRX-$β$ relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX-$β$ diagram.

astro-ph.GA↗

arXiv2017

Dust Properties of [CII] Detected z $\sim$ 5.5 Galaxies: New HST/WFC3 Near-IR Observations

We examine the rest-frame ultra-violet (UV) properties of 10 [CII]$\lambda158\,{\rm μm}$$-$detected galaxies at $z\sim5.5$ in COSMOS using new HST/WFC3 near-infrared imaging. Together with pre-existing $158\,{\rm μm}-$continuum and [CII] line measurements by ALMA, we study their dust attenuation properties on the IRX-$β$ diagram, which connects the total dust emission ($\propto$ IRX=log($L_{FIR}/L_{1600}$)) to the line-of-sight dust column ($\proptoβ$). We find systematically bluer UV continuum spectral slopes ($β$) compared to previous low-resolution ground-based measurements, which relieves some of the tension between models of dust attenuation and observations at high redshifts. While most of the galaxies are consistent with local starburst or Small Magellanic cloud like dust properties, we find galaxies with low IRX values and a large range in $β$ that cannot be explained by models of a uniform dust distribution well mixed with stars. A stacking analysis of Keck/DEIMOS optical spectra indicates that these galaxies are metal-poor with young stellar populations which could significantly alter their spatial dust distribution.

astro-ph.GA↗

arXiv2017

High dense gas fraction in a gas-rich star-forming galaxy at z = 1.2

We report observations of dense molecular gas in the star-forming galaxy EGS 13004291 (z=1.197) using the Plateau de Bure Interferometer. We tentatively detect HCN and HNC (J=2-1) emission when stacked together at ~4sigma significance, yielding line luminosities of L_HCN (J=2-1) =(9 +/- 3) x 10^9 K km s^-1 pc^2 and L_HNC (J=2-1)= (5 +/-2) x 10^9 K km s^-1 pc^2 respectively. We also set 3sigma upper limits of < 7-8 x 10^9 K km s^-1 pc^2 on the HCO+, H2O (3_13-2_20) and HC3N (J=20-19) line luminosities. We serendipitously detect CO emission from two sources at z~1.8 and z~3.2 in the same field of view. We also detect CO(J=2-1) emission in EGS 13004291, showing that the excitation in the previously detected CO(J=3-2) line is subthermal (r_32=0.65 +/- 0.15). We find a line luminosity ratio of L_HCN/L_CO=0.17 +/- 0.07 , as an indicator of the dense gas fraction. This is consistent with the median ratio observed in z>1 galaxies (L_HCN/L_CO=0.16 +/- 0.07) and nearby ULIRGs (L_HCN/L_CO=0.13 +/- 0.03), but higher than in local spirals (L_HCN/L_CO=0.04 +/- 0.02). Although EGS 13004291 lies significantly above the galaxy main sequence at z~1, we do not find an elevated star formation efficiency (traced by L_FIR/L_CO) as in local starbursts, but a value consistent with main-sequence galaxies. The enhanced dense gas fraction, the subthermal gas excitation, and the lower than expected star formation efficiency of the dense molecular gas in EGS 13004291 suggest that different star formation properties may prevail in high-z starbursts. Thus, using L_FIR/L_CO as a simple recipe to measure the star formation efficiency may be insufficient to describe the underlying mechanisms in dense star-forming environments inside the large gas reservoirs.

astro-ph.GA↗

arXiv2017

Molecular Gas Kinematics and Star Formation Properties of the Strongly-Lensed Quasar Host Galaxy RXS J1131-1231

We report observations of CO(J=2-1) and CO(J=3-2) line emission towards the quadruply-lensed quasar RXS J1131-1231 at z = 0.654 obtained using the Plateau de Bure Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Our lens modeling shows that the asymmetry in the double-horned CO(J = 2-1) line profile is mainly a result of differential lensing, where the magnification factor varies from ~3 to ~9 across different kinematic components. The intrinsically symmetric line profile and a smooth source-plane velocity gradient suggest that the host galaxy is an extended rotating disk, with a CO size of R_CO~6 kpc and a dynamical mass of M_dyn~8x10^10 Msun. We also find a secondary CO-emitting source near RXS J1131-1231 whose location is consistent with the optically-faint companion reported in previous studies. The lensing-corrected molecular gas masses are M_gas = (1.4+/-0.3)x10^10 Msun and (2.0+/-0.1)x10^9 Msun for RXS J1131-1231 and the companion, respectively. We find a lensing-corrected stellar mass of M_* = (3+/-1)x10^10 Msun and a star formation rate of SFR_FIR = (120+/-63) Msun yr^-1 , corresponding to a specific SFR and star formation efficiency comparable to z~1 disk galaxies not hosting quasars. The implied gas mass fraction of ~18+/-4% is consistent with the previously-observed cosmic decline since z~2. We thus find no evidence for quenching of star formation in RXS J1131-1231. This agrees with our finding of an elevated MBH/Mbulge ratio of >0.27+0.11% -0.08 compared to the local value, suggesting that the bulk of its black hole mass is largely in place while its stellar bulge is still assembling.

astro-ph.GA↗

arXiv2016

ALMA Reveals Weak [NII] Emission in "Typical" Galaxies and Intense Starbursts at z=5-6

We report interferometric measurements of [NII] 205 um fine-structure line emission from a representative sample of three galaxies at z=5-6 using the Atacama Large (sub)Millimeter Array (ALMA). These galaxies were previously detected in [CII] and far-infrared continuum emission and span almost two orders of magnitude in star formation rate (SFR). Our results show at least two different regimes of ionized inter-stellar medium properties for galaxies in the first billion years of cosmic time, separated by their L_[CII]/L_[NII] ratio. We find extremely low [NII] emission compared to [CII] (L_ [CII]/L_[NII]=68 [+200/-28]) from a "typical" L*_UV star-forming galaxy, likely directly or indirectly (by its effect on the radiation field) related to low dust abundance and low metallicity. The infrared-luminous modestly star-forming Lyman Break Galaxy (LBG) in our sample is characterized by an ionized-gas fraction (L_[CII]/L_[NII]<=20) typical of local star-forming galaxies and shows evidence for spatial variations in its ionized-gas fraction across an extended gas reservoir. The extreme SFR, warm and compact dusty starburst AzTEC-3 shows an ionized fraction higher than expected given its star-formation rate surface density (L_[CII]/L_[NII]=22+/-8) suggesting that [NII] dominantly traces a diffuse ionized medium rather than star-forming HII regions in this type of galaxy. This highest redshift sample of [NII] detections provides some of the first constraints on ionized and neutral gas modeling attempts and on the structure of the inter-stellar medium at z=5-6 in "normal" galaxies and starbursts.

astro-ph.GA↗

arXiv2014

The $m_D-b_M$ Problem of Dirac Gauginos and its Solutions

We examine the effective low-energy theory of the adjoint sector of Dirac gaugino models and its UV completions, and identify the main source of tuning. A holomorphic scalar adjoint mass square (the "$b_M$ term") is generated at the same order (1-loop) as the Dirac gaugino mass (the "$m_D$ term"), leading to the problematic relation $b_M\sim16π^2 m_D^2$, somewhat analogous to the $μ-B_μ$ problem of gauge mediation. We identify the leading operators of the low-energy effective theory contributing to the adjoint sector, and evaluate them in various UV completions, confirming the existence of this problem. We suggest a solution by introducing messenger mixing and tuning the relevant parameters. We also present a novel dynamical model for Dirac gauginos based on a strongly coupled SUSY QCD theory, where the additional adjoint $M$ is identified with a confined meson, the U(1) with a baryon-number like symmetry, and the messengers with the confined baryons. We find a SUSY breaking vacuum with a non-vanishing D-term, which after tuning the messenger mixing angles gives rise to a realistic gaugino and squark sector.

hep-ph↗