Table 2 - uploaded by Bruce Elmegreen
Content may be subject to copyright.
Source publication
Galaxies in the Hubble Ultra Deep Field (UDF) larger than 10 pixels (0.3 arcsec) have been classified according to morphology and their photometric properties are presented. There are 269 spirals, 100 ellipticals, 114 chains, 126 double-clump, 97 tadpole, and 178 clump-cluster galaxies. We also catalogued 30 B-band and 13 V-band drop-outs and calcu...
Similar publications
We present observations of the M87 jet made with the Faint Object Camera on board the Hubble Space Telescope at five epochs between 1994 and 1998. These observations reveal 10 superluminal features within the first 6'' of the jet, with eight of these having apparent speeds in the range 4c-6c. Two additional features within the first arcsecond of th...
We present new results from our search for z~7 galaxies from deep
spectroscopic observations of candidate z-dropouts in the CANDELS fields.
Despite the extremely low flux limits achieved by our sensitive observations,
only 2 galaxies have robust redshift identifications, one from its Lyalpha
emission line at z=6.65, the other from its Lyman-break,...
Equivalent profiles of IC 783, IC 3328 and IC 3653, derived from HST and VLT images, are successfully decomposed using the classical two-component method of Kormendy (1977). Clearly distinguished are a bulge and a faint ex-ponential disk, embedded in the spheroidal component. The blue-light profiles of IC 3328 and IC 3653 point to existence of a ve...
We have undertaken a comprehensive search for both Lyman Alpha Emitters (LAEs) and Lyman Break Galaxies (LBGs) in the SHARDS Survey of the GOODS-N field. SHARDS is a deep imaging survey, made with the 10.4 m Gran Telescopio Canarias (GTC), employing 25 medium band filters in the range from 500 to 941 nm. This is the first time that both LAEs and LB...
We have undertaken a comprehensive search for both Lyman Alpha Emitters (LAEs) and Lyman Break Galaxies (LBGs) in the SHARDS Survey of the GOODS-N field. SHARDS is a deep imaging survey, made with the 10.4 m Gran Telescopio Canarias (GTC), employing 25 medium band filters in the range from 500 to 941 nm. This is the first time that both LAEs and LB...
Citations
... Connecting these constraints on the intrinsic shapes of nearby galaxies with those of their progenitors at high redshift became possible with the advent of the Hubble Space Telescope (HST). Numerous studies have established that the bright, massive population at high redshift already seems to have taken on oblate and spheroidal 3D shapes, albeit with smaller sizes and thicker minor-to-major-axis ratios (Reshetnikov et al. 2003;Elmegreen et al. 2004aElmegreen et al. , 2004bElmegreen et al. , 2005Holden et al. 2012;Chang et al. 2013;van der Wel et al. 2014a;Satoh et al. 2019;Zhang et al. 2019Zhang et al. , 2022Hamilton-Campos et al. 2023). For these bright objects, constraints on gas kinematics through deep emission-line spectroscopy definitively showed the existence of large rotating disks with high random motions at early times (Förster Schreiber et al. 2006Genzel et al. 2006;Law et al. 2009;Kassin et al. 2012;Glazebrook 2013;Wisnioski et al. 2015;Simons et al. 2016Simons et al. , 2017. ...
... Dalcanton & Shectman (1996) argued that these chain galaxies are the edge-on projections of intrinsically oblate disk galaxies. Elmegreen et al. (2004aElmegreen et al. ( , 2004bElmegreen et al. ( , 2005 found more patterns among the peculiar/irregular population and grouped them into additional subclasses: chains, clump clusters, tadpoles, and double clumps (see also van den Bergh 2002; Conselice et al. 2004;Straughn et al. 2006). They, too, argued that chains were the edge-on versions of the rounder clump clusters, with the latter being harder to detect owing to surface brightness dimming. ...
... For all of our mass-redshift bins, the mean ellipticity is high, with μ E 0.75, and the scatter is generally small, with σ E 0.1. These high ellipticities translate to C/A ∼ 0.25, which is thicker than local disks by a factor of ∼2-3 (e.g., Elmegreen et al. 2005). We do not see evidence of strong evolution in C/A over the wide range of redshift and mass considered in Figure 9. ...
The 3D geometries of high-redshift galaxies remain poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in James Webb Space Telescope Cosmic Evolution Early Release Science observations with log M * / M ⊙ = 9.0 – 10.5 at z = 0.5–8.0. We reproduce previous results from the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size, and covariances with samples as small as ∼50 galaxies. We find high 3D ellipticities for all mass–redshift bins, suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be ∼1 for log M * / M ⊙ = 9.0 – 9.5 dwarfs at z > 1 (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a “banana” in the projected b / a – log a diagram with an excess of low- b / a , large- log a galaxies. The dwarf prolate fraction rises from ∼25% at z = 0.5–1.0 to ∼50%–80% at z = 3–8. Our results imply a second kind of disk settling from oval (triaxial) to more circular (axisymmetric) shapes with time. We simultaneously constrain the 3D size–mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar Sérsic indices ( n ∼ 1), nonparametric morphological properties, and specific star formation rates. Both tend to be visually classified as disks or irregular, but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects, and theoretical implications.
... Relying on the nomenclature that has served us at low redshift risks biasing our understanding of this new regime. For example, work carried out in the past by Elmegreen et al. (2005) classified high-redshift galaxies in the Hubble Ultra Deep Field into six main groups: chain, clump cluster, double clump, tadpole, spiral, and elliptical. These groups were determined by eye to match matched previous classifications made by others (Cowie et al. 1995;van den Bergh et al. 1996). ...
Galaxy morphologies provide valuable insights into their formation processes, tracing the spatial distribution of ongoing star formation and encoding signatures of dynamical interactions. While such information has been extensively investigated at low redshift, it is crucial to develop a robust system for characterizing galaxy morphologies at earlier cosmic epochs. Relying solely on nomenclature established for low-redshift galaxies risks introducing biases that hinder our understanding of this new regime. In this paper, we employ variational autoencoders to perform feature extraction on galaxies at z > 2 using JWST/NIRCam data. Our sample comprises 6869 galaxies at z > 2, including 255 galaxies at z > 5, which have been detected in both the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Hubble Space Telescope fields and the Cosmic Evolution Early Release Science Survey done with JWST, ensuring reliable measurements of redshift, mass, and star formation rates. To address potential biases, we eliminate galaxy orientation and background sources prior to encoding the galaxy features, thereby constructing a physically meaningful feature space. We identify 11 distinct morphological classes that exhibit clear separation in various structural parameters, such as the concentration, asymmetry, and smoothness (CAS) metric and M 20 , Sérsic indices, specific star formation rates, and axis ratios. We observe a decline in the presence of spheroidal-type galaxies with increasing redshift, indicating the dominance of disk-like galaxies in the early Universe. We demonstrate that conventional visual classification systems are inadequate for high-redshift morphology classification and advocate the need for a more detailed and refined classification scheme. Leveraging machine-extracted features, we propose a solution to this challenge and illustrate how our extracted clusters align with measured parameters, offering greater physical relevance compared to traditional methods.
... In these studies it was shown that the relative thickness (ratio of vertical to radial scales) of stellar discs at redshift E-mail: vpresh@mail.ru z ∼ 0.5-1 exceeds, on average, the thickness of the discs of nearby spiral galaxies (Reshetnikov, Dettmar & Combes 2003 ;Elmegreen et al. 2005 ;Elmegreen & Elmegreen 2006 ). More recent studies have shown that the vertical scales of the surface-brightness distribution of the discs of spiral galaxies do not show appreciable changes at z ≤ 1 and therefore the e xcess relativ e thickness of distant discs is most likely due to the evolution of their radial scales (Reshetnikov, Usachev & Savchenko 2019 ;Reshetnikov & Usachev 2021 ). ...
We present a sample of 950 edge-on spiral galaxies found with the use of an artificial neural network in the Hubble Space Telescope COSMOS field. This is currently the largest sample of distant edge-on galaxies. For all galaxies we analysed the 2D brightness distributions in the F814W filter and measured the radial and vertical exponential scales (h and hz correspondingly) of the brightness distribution. By comparing the characteristics of distant galaxies with those of nearby objects, we conclude that thin stellar discs with h/hz ≥ 10 at z ≈ 0.5 should be rarer than today. Both exponential scales of the stellar disc show evidence of luminosity-dependent evolution: in faint galaxies the h and hz values do not change with z, in bright (and massive) spiral galaxies both scales, on average, grow towards our epoch.
... On the contrary, another scenario that was proposed more recently assumes the local thick disks were initially formed to be thick (Brook et al. 2004;Bournaud et al. 2009). This scenario is supported by the fact that galaxies in the early Universe, when the local thick disk stars are expected to form, are much more turbulent that the local galaxies given their large velocity dispersion (e.g., Weiner et al. 2006;Shapiro et al. 2008;Simons et al. 2016;Übler et al. 2019) and disturbed and clumpy morphology (e.g., Elmegreen et al. 2005Elmegreen et al. , 2009. ...
Although a thick disk is a structure prevalent in local disk galaxies and also present in our home Galaxy, its formation and evolution are still unclear. Whether the thick disk is born thick and/or gradually heated to be thick after formation is under debate. To disentangle these two scenarios, one effective approach is to inspect the thickness of young disk galaxies in the high-redshift Universe. In this work we study the vertical structure of 191 edge-on galaxies spanning redshift from 0.2 to 5 using JWST NIRCAM imaging observations. For each galaxy, we retrieve the vertical surface brightness profile at 1 R e and fit a sech ² function that has been convolved with the line spread function. The obtained scale height of galaxies at z > 1.5 shows no clear dependence on redshift, with a median value in remarkable agreement with that of the Milky Way’s thick disk. This suggests that local thick disks are already thick when they were formed in early times and secular heating is unlikely to be the main driver of thick disk formation. For galaxies at z < 1.5, however, the disk scale height decreases systematically toward lower redshift, with low-redshift galaxies having comparable scale height with that of the Milky Way’s thin disk. This cosmic evolution of disk thickness favors an upside-down formation scenario of galaxy disks.
... The build-up of structure in the very early Universe (prior to cosmic noon) is extremely chaotic, with the infall of gas causing immense star formation in large clumps, and lots of galaxy mergers making the definition of galaxy structure difficult (as demonstrated by, for example, Lotz et al. 2004;Elmegreen et al. 2005;Lee et al. 2013). By cosmic noon, however, structure is sufficiently well defined to describe galaxies in the context of substructures such as bulges and disks. ...
We present the first look at star formation histories of galaxy components using ProFuse, a new technique to model the 2D distribution of light across multiple wavelengths using simultaneous spectral and spatial fitting of purely imaging data. We present a number of methods to classify galaxies structurally/morphologically, showing the similarities and discrepancies between these schemes. Rather than identifying the best-performing scheme, we use the spread of classifications to quantify uncertainty in our results. We study the cosmic star formation history (CSFH), forensically derived using ProFuse with a sample of ~7,000 galaxies from the Galaxy And Mass Assembly (GAMA) survey. Remarkably, the forensic CSFH recovered via both our method (ProFuse) and traditional SED fitting (ProSpect) are not only exactly consistent with each other over the past 8 Gyr, but also with the in-situ CSFH measured using ProSpect. Furthermore, we separate the CSFH by contributions from spheroids, bulges and disks. While the vast majority (70%) of present-day star formation takes place in the disk population, we show that 50% of the stars that formed at cosmic noon (8-12 Gyr ago) now reside in spheroids, and present-day bulges are composed of stars that were primarily formed in the very early Universe, with half their stars already formed ~12 Gyr ago.
... Relying on the nomenclature that has served us at low-redshift risks biasing our understanding of this new regime. For example, work carried out in the past by Elmegreen et al. (2005) classified high redshift galaxies in the Hubble Ultra Deep Field into 6 main groups; chain, clump cluster, double clump, tadpole, spiral and elliptical. These groups were determined by eye to match matched previous classifications by others (Cowie et al. 1995;van den Bergh et al. 1996). ...
Galaxy morphologies provide valuable insights into their formation processes, tracing the spatial distribution of ongoing star formation and encoding signatures of dynamical interactions. While such information has been extensively investigated at low redshift, it is crucial to develop a robust system for characterising galaxy morphologies at earlier cosmic epochs. Relying solely on the nomenclature established for low-redshift galaxies risks introducing biases that hinder our understanding of this new regime. In this paper, we employ variational auto-encoders to perform feature extraction on galaxies at z $>$ 2 using JWST/NIRCam data. Our sample comprises 6869 galaxies at z $>$ 2, including 255 galaxies z $>$ 5, which have been detected in both the CANDELS/HST fields and CEERS/JWST, ensuring reliable measurements of redshift, mass, and star formation rates. To address potential biases, we eliminate galaxy orientation and background sources prior to encoding the galaxy features, thereby constructing a physically meaningful feature space. We identify 11 distinct morphological classes that exhibit clear separation in various structural parameters, such as CAS-$M_{20}$, S\'ersic indices, specific star formation rates, and axis ratios. We observe a decline in the presence of spheroidal-type galaxies with increasing redshift, indicating a dominance of disk-like galaxies in the early universe. We demonstrate that conventional visual classification systems are inadequate for high-redshift morphology classification and advocate the need for a more detailed and refined classification scheme. Leveraging machine-extracted features, we propose a solution to this challenge and illustrate how our extracted clusters align with measured parameters, offering greater physical relevance compared to traditional methods.
... However, at z > 1, these optical surveys probed the rest-frame UV light of galaxies and found that very large fractions of distant galaxies had peculiar or clumpy morphologies, which suggested at the time that the Hubble sequence had not yet formed at these early times (e.g., Abraham et al. 1996). Investigations using near-infrared observations with NICMOS, sensitive to the rest-frame optical structure of galaxies, found that galaxies beyond z ∼ 1 presented a wide diversity of morphologies, including many objects that were compact or irregular but also those that were morphologically mature spirals and ellipticals (e.g., van Dokkum & Franx 2001; Stanford et al. 2004;Daddi et al. 2005;Elmegreen et al. 2005;Papovich et al. 2005). ...
... The distribution of the axis ratios is shown in the right panel of Figure 4 and in Figure 5 and offers another way to compare our visual morphologies to a quantitative measurement. A population of disks with exponential profiles and random orientations is expected to have a relatively flat distribution of axis ratios that falls off at low values, while triaxial ellipsoids are expected to have a distribution that is peaked at higher values, b/a ∼ 0.6 (e.g., Elmegreen et al. 2005 Figure 6 shows the axis ratio as a function of effective radius split into several redshift bins. In each redshift bin from z = 3 to 6, the spheroid-only galaxies have the smallest median effective radius and largest median axis ratios, suggestive of a population of true triaxial ellipsoids. ...
... The lines show the boundaries between disk and elliptical galaxies (dashed-dotted) and mergers (dashed) from Lotz et al. (2008a). The colors indicate the different combinations of the main morphological class chosen by two out of three people during the visual classifications, as described in Section 4.1 and Figure 2. detect than edge-on disks at the magnitude limit (e.g., Elmegreen et al. 2005), and the presence of dust can impact the measured axis ratios (Padilla & Strauss 2008). The size of the current sample does not allow binning by mass, luminosity, or finer morphology groupings; however, future work with larger sample sizes will allow greater exploration of this parameter space. ...
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z = 3–9 using early James Webb Space Telescope (JWST) CEERS NIRCam observations. Our sample consists of 850 galaxies at z > 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at z > 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at z = 3, and this fraction drops to ∼30% at z = 6–9, while galaxies with spheroids make up ∼30%–40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%–50%), while those that are purely irregular increases from ∼12% to ∼20% at z > 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.
... Gas accretion onto galaxies drives their average star formation rates (SFRs; Finlator & Davé 2008;Brooks et al. 2009;Combes 2014), with excess local accretion possibly connected to major bursts (Sánchez Almeida et al. 2014a, 2014bCeverino et al. 2016). Tadpoles (van den Bergh et al. 1996;Elmegreen et al. 2005), or cometary galaxies (Markarian 1969;Loose & Thuan 1985;Cairós et al. 2001), are gas-rich dwarfs with one giant star-forming region that looks like the head of a tadpole when the galaxy is viewed at some inclination; the rest of the disk comprises the tail. This morphology is common at high redshift, where it is found in ∼10% of resolved galaxies (van den Bergh et al. 1996;Elmegreen et al. 2005;Straughn et al. 2006;Windhorst et al. 2006), but it is rare locally at less than 0.2% (Elmegreen et al. 2012). ...
... Tadpoles (van den Bergh et al. 1996;Elmegreen et al. 2005), or cometary galaxies (Markarian 1969;Loose & Thuan 1985;Cairós et al. 2001), are gas-rich dwarfs with one giant star-forming region that looks like the head of a tadpole when the galaxy is viewed at some inclination; the rest of the disk comprises the tail. This morphology is common at high redshift, where it is found in ∼10% of resolved galaxies (van den Bergh et al. 1996;Elmegreen et al. 2005;Straughn et al. 2006;Windhorst et al. 2006), but it is rare locally at less than 0.2% (Elmegreen et al. 2012). Based on simulations by Ceverino et al. (2016) of low-metallicity gas infall onto disk galaxies, which typically triggers a burst of star formation near one end of the disk, we expect that tadpole galaxies would appear disk-like if viewed face-on, with at least one prominent star-forming region. ...
Tadpole galaxies are metal-poor dwarfs with typically one dominant star-forming region, giving them a head–tail structure when inclined. A metallicity drop in the head suggests that gas accretion with even lower metallicity stimulated the star formation. Here we present multiband Hubble Space Telescope WFC3 and Advanced Camera for Surveys images of four nearby (<25 Mpc) tadpoles, SBS0, SBS1, Kiso3867, and UM461, selected for their clear metallicity drops shown in previous spectroscopic studies. The properties of the star complexes and compact clusters are measured. Each galaxy contains from three to 10 young stellar complexes with 10 ³ –10 ⁵ M ⊙ of stars ∼3–10 Myr old. Between the complexes, the disk has a typical age of ∼3 Gyr. Numerous star clusters cover the galaxies, both inside and outside the complexes. The combined cluster mass function, made by normalizing the masses and counts before stacking, is a power law with a slope of −1.12 ± 0.14 on a log–log plot and the combined distribution function of cluster lifetime decays with age as t −0.65±0.24 . A comparison between the summed theoretical Lyman continuum (LyC) emission from all the clusters, given their masses and ages, is comparable to or exceeds the LyC needed to excite the observed H α in some galaxies, suggesting LyC absorption by dust or undetected gas in the halo, or perhaps galaxy escape.
... However, at z > 1, these optical surveys probed the rest-frame UV light of galaxies and found that very large fractions of distant galaxies had peculiar or clumpy morphologies, which suggested at the time that the Hubble sequence had not yet formed at these early times (e.g., Abraham et al. 1996). Investigations using near-infrared observations with NICMOS, sensitive to the rest-frame optical structure of galaxies, found that galaxies beyond z ∼ 1 presented a wide diversity of morphologies, including many objects that were compact or irregular, but also those that were morphologically mature spirals and ellipticals (e.g., van Dokkum & Franx 2001;Stanford et al. 2004;Papovich et al. 2005;Daddi et al. 2005;Elmegreen et al. 2005). ...
... The distribution of the axis ratios is shown in the right panel of Figure 6 and in 7 and offers another way to compare our visual morphologies to a quantitative measurement. A population of disks with exponential profiles and random orientations is expected to have a relatively flat distribution of axis ratios that falls off at low values while triaxial ellipsoids are expected to have a distribution that is peaked at higher values, b/a ∼ 0.6, (e.g., Elmegreen et al. 2005;Ravindranath et al. 2006;Padilla & Strauss 2008;Law et al. 2012;Robertson et al. 2022). ...
... For example, it has been shown that the distribution of axis ratios have a strong dependence on the mass and luminosity of the galaxy population (e.g., Padilla & Strauss 2008;Zhang et al. 2019). Galaxy orientation also plays an important role in this distribution, as face-on disks may be more difficult to detect than edge-on disks at the magnitude limit (e.g., Elmegreen et al. 2005) and the presence of dust can impact the measured axis ratios (Padilla & Strauss 2008). The size of the current sample does not allow binning by mass, luminosity, or finer morphology groupings, however, future work with larger sample sizes will allow greater exploration of this parameter space. ...
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z=3-9 using early JWST CEERS NIRCam observations. Our sample consists of 850 galaxies at z>3 detected in both CANDELS HST imaging and JWST CEERS NIRCam images to enable a comparison of HST and JWST morphologies. Our team conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. We also measure quantitative morphologies using the publicly available codes across all seven NIRCam filters. Using these measurements, we present the fraction of galaxies of each morphological type as a function of redshift. Overall, we find that galaxies at z>3 have a wide diversity of morphologies. Galaxies with disks make up a total of 60\% of galaxies at z=3 and this fraction drops to ~30% at z=6-9, while galaxies with spheroids make up ~30-40% across the whole redshift range and pure spheroids with no evidence for disks or irregular features make up ~20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (~40-50%), while those that are purely irregular increases from ~12% to ~20% at z>4.5. We note that these are apparent fractions as many selection effects impact the visibility of morphological features at high redshift. The distributions of S\'ersic index, size, and axis ratios show significant differences between the morphological groups. Spheroid Only galaxies have a higher S\'ersic index, smaller size, and higher axis ratio than Disk/Irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study and further work with large samples at higher redshift is needed to quantify when these features first formed.
... E-mail: uros.mestric@inaf.it In the last few decades, different studies revealed that high-redshift star-forming galaxies (SFGs, z ∼ 1-3) have a clumpy morphology, which differs from the spiral-like structure of most star-forming galaxies in the local Universe (e.g Cowie, Hu & Songaila 1995 ;Elmegreen et al. 2005Elmegreen et al. , 2007Conselice 2014 ). High-redshift clumps have masses 10 7 -10 9 M , sizes ∼ 0 . 1 -1kpc, and usually they are characterized by a high star formation rate (e.g. ...
We study the physical properties (size, stellar mass, luminosity, star formation rate) and scaling relations for a sample of 166 star-forming clumps with redshift z ∼ 2 − 6.2. They are magnified by the Hubble Frontier Field galaxy cluster MACS J0416 and have robust lensing magnification (2 ≲ μ ≲ 82) computed by using our high-precision lens model, based on 182 multiple images. Our sample extends by ∼3 times the number of spectroscopically-confirmed lensed clumps at z ≳ 2. We identify clumps in ultraviolet continuum images and find that, whenever the effective spatial resolution (enhanced by gravitational lensing) increases, they fragment into smaller entities, likely reflecting the hierarchically-organized nature of star formation. Kpc-scale clumps, most commonly observed in field, are not found in our sample. The physical properties of our sample extend the parameter space typically probed by z ≳ 1 field observations and simulations, by populating the low mass (M⋆ ≲ 107 M⊙), low star formation rate (SFR ≲ 0.5 M⊙ yr−1), and small size (Reff ≲ 100 pc) regime. The new domain probed by our study approaches the regime of compact stellar complexes and star clusters. In the mass-size plane, our sample spans the region between galaxies and globular clusters, with a few clumps in the region populated by young star clusters and globular-clusters. For the bulk of our sample, we measure star-formation rates which are higher than those observed locally in compact stellar systems, indicating different conditions for star formation at high redshift than in the local Universe.
