arXiv subjects

Marc Verheijen

Publications and source records attributed to Marc Verheijen.

At least 19 recordsLinked to original sources

arXiv2026

Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET)

[ABRIDGED] Galaxy evolution is shaped by internal and external mechanisms that regulate the baryon cycle and star formation activity. We present a theoretical framework based on the GAlaxy Evolution and Assembly (GAEA) semi-analytic model. We extracted portions of simulated volumes that include isolated galaxies, pairs, group, and filament members at z ~ 0, specifically avoiding massive clusters. Galaxies were classified using both intrinsic (halo-based) and observational (2D projected) parameterizations, reconstructing their environmental histories from z = 2 and identifying mergers, tidal interactions, ram pressure stripping (RPS), and starvation. 2D information decreases isolated and group fractions while doubles pairs. More than half of galaxies remain unaffected by the investigated processes since z = 2. Among affected galaxies, mergers dominate at high stellar masses (40-60% at log(M*/Msun) > 10.5). Tidal interactions are less frequent, and their incidence increases with stellar mass. RPS dominates in groups and filaments at intermediate masses (~50%), while starvation ranges from 20 to 30%. The incidence of the different mechanisms depends strongly on both mass and environment, though their imprints on global properties are often subtle. Distinct evolutionary pathways emerge: log(M*/Msun) < 9.5, galaxies in groups and filaments have a faster mass growth than galaxies in the other environments, especially those undergoing starvation, mergers and, to less extent, RPS. Differences are reduced moving to higher masses, where no clear dependence on physical mechanism emerge, even though at these masses a clear star formation suppression is evident in mergers and starved galaxies. This theoretical investigation provides essential context for the recently started multi-wavelength program Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET), which we introduce here.

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arXiv2025

Why the Northern Hemisphere Needs a 30-40m Telescope and the Science at Stake: Ultra-Low-Mass Dwarf Galaxies Across the Boreal Cosmic Web

Dwarf galaxies dominate the galaxy population in the nearby Universe and occupy the regime where feedback, reionization, and environment exert their strongest influence on galaxy formation. Despite their importance, detailed spectroscopic constraints on the faintest dwarfs are currently limited to a handful of systems in the Local Volume, leaving the role of large-scale environment essentially unexplored at ultra-low stellar masses. A northern 30-40m class telescope equipped with a multiplexed optical integral-field spectrograph will enable a systematic, spatially resolved spectroscopic census of dwarf galaxies with $M_\star \sim 10^{5}-10^{7} M_\odot$ across a wide range of environments. A deep survey of the Coma Cluster, combined with targeted observations of dwarfs in clusters, groups, filaments, and low-density regions, will map star formation histories, chemical enrichment, and internal kinematics at unprecedented depth. This program will directly test models of dark-matter physics, early-Universe feedback, and environmental quenching in the lowest-mass galaxies, establishing dwarf galaxies as precision probes of both galaxy formation and fundamental physics.

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arXiv2024

Looking At the Distant Universe with the MeerKAT Array: the HI Mass Function in the Local Universe

We present measurements of the neutral atomic hydrogen (HI) mass function (HIMF) and cosmic HI density ($\Omega_{\rm HI}$) at $0 \leq z \leq 0.088$ from the Looking at the Distant Universe with MeerKAT Array (LADUMA) survey. Using LADUMA Data Release 1 (DR1), we analyze the HIMF via a new "recovery matrix" (RM) method that we benchmark against a more traditional Modified Maximum Likelihood (MML) method. Our analysis, which implements a forward modeling approach, corrects for survey incompleteness and uses extensive synthetic source injections to ensure robust estimates of the HIMF parameters and their associated uncertainties. This new method tracks the recovery of sources in mass bins different from those in which they were injected and incorporates a Poisson likelihood in the forward modeling process, allowing it to correctly handle uncertainties in bins with few or no detections. The application of our analysis to a high-purity subsample of the LADUMA DR1 spectral line catalog in turn mitigates any possible biases that could result from the inconsistent treatment of synthetic and real sources. For the surveyed redshift range, the recovered Schechter function normalization, low-mass slope, and "knee" mass are $\phi_\ast = 3.56_{-1.92}^{+0.97} \times 10^{-3}$ Mpc$^{-3}$ dex$^{-1}$, $\alpha = -1.18_{-0.19}^{+0.08}$, and $\log(M_\ast/M_\odot) = 10.01_{-0.12}^{+0.31}$, respectively, which together imply a comoving cosmic HI density of $\Omega_{\rm HI}=3.09_{-0.47}^{+0.65}\times 10^{-4}$. Our results show consistency between RM and MML methods and with previous low-redshift studies, giving confidence that the cosmic volume probed by LADUMA, even at low redshifts, is not an outlier in terms of its HI content.

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arXiv2023

BUDHIES IV: Deep 21-cm neutral Hydrogen, optical and UV imaging data of Abell 963 and Abell 2192 at z $\simeq$ 0.2

In this paper, we present data from the Blind Ultra-Deep HI Environmental Survey (BUDHIES), which is a blind 21-cm HI spectral line imaging survey undertaken with the Westerbork Synthesis Radio Telescope (WSRT). Two volumes were surveyed, each with a single pointing and covering a redshift range of 0.164 < z < 0.224. Within these two volumes, this survey targeted the clusters Abell 963 and Abell 2192, which are dynamically different and offer unique environments to study the process of galaxy evolution within clusters. With an integration time of 117x12h on Abell 963 and 72x12h on Abell 2192, a total of 166 galaxies were detected and imaged in HI. While the clusters themselves occupy only 4 per cent of the 73,400 Mpc$^3$ surveyed by BUDHIES, most of the volume consists of large-scale structures in which the clusters are embedded, including foreground and background overdensities and voids. We present the data processing and source detection techniques and counterpart identification based on a wide-field optical imaging survey using the Isaac Newton Telescope (INT) and deep ultra-violet GALEX imaging. Finally, we present HI and optical catalogues of the detected sources as well as atlases of their global HI properties, which include integrated column density maps, position-velocity diagrams, global HI profiles, and optical and UV images of the HI sources.

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arXiv2023

UV and H$α$ HST observations of 6 GASP jellyfish galaxies

Star-forming, H$α$-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram-pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination of broad-band filters and a narrow-band Hα filter. HST observations are needed to study the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will be used to study the clump scaling relations, the universality of the star formation process and verify whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis: the UVIS high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions of the galaxies and of the substructures in the galaxy disks; we found clear signatures of stripping in regions very close in projection to the galactic disk; the star-forming regions in the stripped tails are extremely bright and compact while we did not detect a significant number of star-forming clumps outside those detected by MUSE. The paper finally presents the development plan for the project.

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arXiv2022

LADUMA: Discovery of a luminous OH megamaser at $z > 0.5$

In the local Universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (HI), radio surveys to probe the cosmic evolution of HI in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep HI survey, we report the first untargeted detection of an OHM at $z > 0.5$, LADUMA J033046.20$-$275518.1 (nicknamed "Nkalakatha"). The host system, WISEA J033046.26$-$275518.3, is an infrared-luminous radio galaxy whose optical redshift $z \approx 0.52$ confirms the MeerKAT emission line detection as OH at a redshift $z_{\rm OH} = 0.5225 \pm 0.0001$ rather than HI at lower redshift. The detected spectral line has 18.4$σ$ peak significance, a width of $459 \pm 59\,{\rm km\,s^{-1}}$, and an integrated luminosity of $(6.31 \pm 0.18\,{\rm [statistical]}\,\pm 0.31\,{\rm [systematic]}) \times 10^3\,L_\odot$, placing it among the most luminous OHMs known. The galaxy's far-infrared luminosity $L_{\rm FIR} = (1.576 \pm 0.013) \times 10^{12}\,L_\odot$ marks it as an ultra-luminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step towards a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts.

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arXiv2021

GASP XXXVIII: The LOFAR-MeerKAT-VLA view on the non-thermal side of a jellyfish galaxy

Ram pressure stripping is a crucial evolutionary driver for cluster galaxies. It is thought to be able to accelerate the evolution of their star formation, trigger the activity of their central active galactic nucleus (AGN) and the interplay between the galactic and environmental gas, and eventually dissipate their gas reservoir. We explored the outcomes of ram pressure stripping by studying the non-thermal radio emission of the jellyfish galaxy JW100 in the cluster Abell 2626 ($z=0.055$) by combining LOFAR, MeerKAT, and VLA observations from 0.144 to 5.5 GHz. We studied the integrated spectra of the stellar disk, the stripped tail and the AGN, mapped the spectral index over the galaxy, and constrained the magnetic field intensity to be between 11 and 18 $μ$G in the disk and $<10$ $μ$G in the tail. The stellar disk radio emission is dominated by a radiatively old plasma, likely related to an older phase of high star formation rate. This suggests that the star formation was quickly quenched by a factor of 4 in a few $10^7$ yr. The radio emission in the tail is consistent with the stripping scenario, where the radio plasma originally accelerated in the disk is then displaced in the tail. The morphology of the radio and X-ray emissions supports the scenario of accretion of the magnetized environmental plasma onto the galaxy. The AGN non-thermal spectrum indicates that the relativistic electron acceleration may have occurred simultaneously with a central ionized gas outflow, thus suggesting a physical connection between the two processes.

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arXiv2021

The dwarf galaxy population in nearby clusters from the KIWICS survey

We analyse a sample of twelve galaxy clusters, from the Kapteyn IAC WEAVE INT Cluster Survey (KIWICS) looking for dwarf galaxy candidates. By using photometric data in the $r$ and $g$ bands from the Wide Field Camera (WFC) at the 2.5-m Isaac Newton telescope (INT), we select a sample of bright dwarf galaxies (M$_r$ $\leq$ -15.5 mag) in each cluster and analyse their spatial distribution, stellar colour, and as well as their Sérsic index and effective radius. We quantify the dwarf fraction inside the $R_{200}$ radius of each cluster, which ranges from $\sim$ 0.7 to $\sim$ 0.9. Additionally, when comparing the fraction in the inner region with the outermost region of the clusters, we find that the fraction of dwarfs tends to increase going to the outer regions. We also study the clustercentric distance distribution of dwarf and giant galaxies (M$_r$ $<$ -19.0 mag), and in half of the clusters of our sample, the dwarfs are distributed in a statistically different way as the giants, with the giant galaxies being closer to the cluster centre. We analyse the stellar colour of the dwarf candidates and quantify the fraction of blue dwarfs inside the $R_{200}$ radius, which is found to be less than $\sim$ 0.4, but increases with distance from the cluster centre. Regarding the structural parameters, the Sérsic index for the dwarfs we visually classify as early type dwarfs tends to be higher in the inner region of the cluster. These results indicate the role that the cluster environment plays in shaping the observational properties of low-mass halos.

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arXiv2014

Project overview and update on WEAVE: the next generation wide-field spectroscopy facility for the William Herschel Telescope

We present an overview of and status report on the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT). WEAVE principally targets optical ground-based follow up of upcoming ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single spectrograph, with a pair of 8k(spectral) x 6k (spatial) pixel cameras, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the final design and early procurement phase, with commissioning at the telescope expected in 2017.

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arXiv2014

The triggering of starbursts in low-mass galaxies

Strong bursts of star formation in galaxies may be triggered either by internal or external mechanisms. We study the distribution and kinematics of the HI gas in the outer regions of 18 nearby starburst dwarf galaxies, that have accurate star-formation histories from HST observations of resolved stellar populations. We find that starburst dwarfs show a variety of HI morphologies, ranging from heavily disturbed HI distributions with major asymmetries, long filaments, and/or HI-stellar offsets, to lopsided HI distributions with minor asymmetries. We quantify the outer HI asymmetry for both our sample and a control sample of typical dwarf irregulars. Starburst dwarfs have more asymmetric outer HI morphologies than typical irregulars, suggesting that some external mechanism triggered the starburst. Moreover, galaxies hosting an old burst (>100 Myr) have more symmetric HI morphologies than galaxies hosting a young one (<100 Myr), indicating that the former ones probably had enough time to regularize their outer HI distribution since the onset of the burst. We also investigate the nearby environment of these starburst dwarfs and find that most of them ($\sim$80$\%$) have at least one potential perturber at a projected distance <200 kpc. Our results suggest that the starburst is triggered either by past interactions/mergers between gas-rich dwarfs or by direct gas infall from the IGM.

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arXiv2014

Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby objects

We investigate the dynamics of starbursting dwarf galaxies, using both new and archival HI observations. We consider 18 nearby galaxies that have been resolved into single stars by HST observations, providing their star formation history and total stellar mass. We find that 9 objects have a regularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2 show unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a velocity gradient along the minor axis of the HI disk, that we interpret as strong radial motions. For galaxies with a regularly rotating disk we derive rotation curves, while for galaxies with a kinematically disturbed disk we estimate the rotation velocities in their outer parts. We derive baryonic fractions within about 3 optical scale lengths and find that, on average, baryons constitute at least 30$\%$ of the total mass. Despite the star formation having injected $\sim$10$^{56}$ ergs in the ISM in the last $\sim$500 Myr, these starbursting dwarfs have both baryonic and gas fractions similar to those of typical dwarf irregulars, suggesting that they did not eject a large amount of gas out of their potential wells.

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arXiv2014

Dynamics of Starbursting Dwarf Galaxies. II. UGC 4483

UGC 4483 is a nearby Blue Compact Dwarf (BCD) galaxy. HST observations have resolved the galaxy into single stars and this has led to the derivation of its star formation history and to a direct estimate of its stellar mass. We have analysed archival VLA observations of the 21 cm line and found that UGC 4483 has a steeply-rising rotation curve which flattens in the outer parts at a velocity of ~20 km/s. Radial motions of ~5 km/s may also be present. As far as we know, UGC 4483 is the lowest-mass galaxy with a differentially rotating HI disk. The steep rise of the rotation curve indicates that there is a strong central concentration of mass. We have built mass models using the HST information on the stellar mass to break the disk-halo degeneracy: old stars contribute ~50$%$ of the observed rotation velocity at 2.2 disk scale-lengths. Baryons (gas and stars) constitute an important fraction of the total dynamical mass. These are striking differences with respect to typical dwarf irregular galaxies (dIrrs), which usually have slowly-rising rotation curves and are thought to be entirely dominated by dark matter. BCDs appear to be different from non-starbursting dIrrs in terms of their HI and stellar distributions and their internal dynamics. To their high central surface brightnesses and high central HI densities correspond strong central rotation-velocity gradients. This implies that the starburst is closely related with the gravitational potential and the concentration of gas. We discuss the implications of our results on the properties of the progenitors/descendants of BCDs.

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arXiv2013

Evolution of dwarf galaxies: a dynamical perspective

For a rotating galaxy, the inner circular-velocity gradient d_{R}V(0) provides a direct estimate of the central dynamical mass density, including gas, stars, and dark matter. We consider 60 low-mass galaxies with high-quality HI and/or stellar rotation curves (including starbursting dwarfs, irregulars, and spheroidals), and estimate d_{R}V(0) as V(R_d)/R_d, where R_d is the galaxy scale-length. For gas-rich dwarfs, we find that V(R_d)/R_d correlates with the central surface brightness mu(0), the mean atomic gas surface density Sigma_gas, and the star formation rate surface density Sigma_SFR. Starbursting galaxies, such as blue compact dwarfs (BCDs), generally have higher values of V(R_d)/R_d than dwarf irregulars, suggesting that the starburst is closely related to the inner shape of the potential well. There are, however, some "compact" irregulars with values of V(R_d)/R_d similar to BCDs. Unless a redistribution of mass takes place, BCDs must evolve into compact irregulars. Rotating spheroidals in the Virgo cluster follow the same correlation between V(R_d)/R_d and mu(0) as gas-rich dwarfs. They have values of V(R_d)/R_d comparable to those of BCDs and compact irregulars, pointing at evolutionary links between these types of dwarfs. Finally, we find that, similarly to spiral galaxies and massive starbursts, the star-formation activity in dwarfs can be parametrized as Sigma_SFR = epsilon*Sigma_gas/t_orb, where t_orb is the orbital time and epsilon = 0.02.

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arXiv2013

A scaling-relation for disc galaxies: circular-velocity gradient versus central surface brightness

For disc galaxies, a close relation exists between the distribution of light and the shape of the rotation curve. We quantify this relation by measuring the inner circular-velocity gradient d_{R}V(0) for spiral and irregular galaxies with high-quality rotation curves. We find that d_{R}V(0) correlates with the central surface brightness mu_{0} over more than two orders of magnitude in d_{R}V(0) and four orders of magnitudes in mu_{0}. This is a scaling-relation for disc galaxies. It shows that the central stellar density of a galaxy closely relates to the inner shape of the potential well, also for low-luminosity and low-surface-brightness galaxies that are expected to be dominated by dark matter.

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arXiv2011

Dynamics of Starbursting Dwarf Galaxies: I Zw 18

I Zw 18 is a prototype Blue Compact Dwarf (BCD), characterized by a strong starburst and extremely low metallicity (Z ~ 0.02 Zsun). It has long been considered a candidate young galaxy in the Local Universe, but recent studies indicate the presence of old stars. We analysed archival VLA observations of the 21 cm line and found that the HI associated to the starburst region forms a compact fast-rotating disk. The HI column densities are very high, up to ~50-100 Msun/pc^2 (~0.6-1.2 x 10^22 atoms/cm^2). The rotation curve is flat with a steep rise in the inner parts, indicating the presence of a strong central concentration of mass. Mass models with a dark matter halo show that baryons may dominate the gravitational potential in the inner regions. A radial inflow/outflow motion of ~15 km/s is also present. I Zw 18 appears structurally different from typical dwarf irregulars in terms of gas distribution, stellar distribution and dynamics. It may be considered as a "miniature" high-surface-brightness disk galaxy. These dynamical properties must be tightly related to the starburst. They also shed new light on the question of the descendants of BCDs. There is also extended HI emission towards the outlying stellar complex I Zw 18 C and a ~13.5 kpc HI tail. An interaction/merger between gas-rich dwarfs is the most likely explanation for the starburst.

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arXiv2011

LOFAR and APERTIF surveys of the radio sky: probing shocks and magnetic fields in galaxy clusters

At very low frequencies, the new pan-European radio telescope LOFAR is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. The revolutionary APERTIF phased arrays that are about to be installed on the Westerbork radio telescope (WSRT) will dramatically increase the survey speed for the WSRT. Combined surveys with these two facilities will deeply chart the northern sky over almost two decades in radio frequency from \sim 15 up to 1400 MHz. Here we briefly describe some of the capabilities of these new facilities and what radio surveys are planned to study fundamental issues related the formation and evolution of galaxies and clusters of galaxies. In the second part we briefly review some recent observational results directly showing that diffuse radio emission in clusters traces shocks due to cluster mergers. As these diffuse radio sources are relatively bright at low frequencies, LOFAR should be able to detect thousands of such sources up to the epoch of cluster formation. This will allow addressing many question about the origin and evolution of shocks and magnetic fields in clusters. At the end we briefly review some of the first and very preliminary LOFAR results on clusters.

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arXiv2010

Westerbork Ultra-Deep Survey of HI at z=0.2

In this contribution, we present some preliminary observational results from the completed ultra-deep survey of 21cm emission from neutral hydrogen at redshifts z=0.164-0.224 with the Westerbork Synthesis Radio Telescope. In two separate fields, a total of 160 individual galaxies has been detected in neutral hydrogen, with HI masses varying from 1.1x10^9 to 4.0x10^10 Msun. The largest galaxies are spatially resolved by the synthesized beam of 23x37 arcsec^2 while the velocity resolution of 19 km/s allowed the HI emission lines to be well resolved. The large scale structure in the surveyed volume is traced well in HI, apart from the highest density regions like the cores of galaxy clusters. All significant HI detections have obvious or plausible optical counterparts which are usually blue late-type galaxies that are UV-bright. One of the observed fields contains a massive Butcher-Oemler cluster but none of the associated blue galaxies has been detected in HI. The data suggest that the lower-luminosity galaxies at z=0.2 are more gas-rich than galaxies of similar luminosities at z=0, pending a careful analysis of the completeness near the detection limit. Optical counterparts of the HI detected galaxies are mostly located in the 'blue cloud' of the galaxy population although several galaxies on the 'red sequence' are also detected in HI. These results hold great promise for future deep 21cm surveys of neutral hydrogen with MeerKAT, APERTIF, ASKAP, and ultimately the Square Kilometre Array.

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arXiv2010

The latest on Apertif

We describe a Phased Array Feed (PAF) system, called Apertif, which will be installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous field of view of the WSRT 8 deg^2 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications ranging from deep surveys of the northern sky of HI and OH emission and polarised continuum to efficient searches for pulsars and transients. We present results obtained with a prototype PAF installed in one of the WSRT dishes. These results demonstrate that at decimetre wavelengths PAFs have excellent performance and that even for a single beam on the sky they outperform single feed radio dishes. PAFs turn radio telescopes into very effective survey instruments. Apertif is now fully funded and the community is invited to express their interest in using Apertif (http://www.astron.nl/radio-observatory/call-expressions-interest-apertif-surveys )

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