Recession Velocity Research Articles

Peculiar velocities in the local Universe: comparison of different models and the implications for H0 and dark matter

ABSTRACT When measuring the value of the Hubble parameter, H0, it is necessary to know the recession velocity free of the effects of peculiar velocities. In this work, we study different models of peculiar velocity in the local Universe. In particular, we compare models based on density reconstruction from galaxy redshift surveys and kernel smoothing of peculiar velocity data. The velocity field from the density reconstruction is obtained using the 2M++ galaxy redshift compilation, which is compared to two adaptive kernel-smoothed velocity fields: the first obtained from the 6dF Fundamental Plane sample and the other using a Tully–Fisher catalogue obtained by combining SFI++ and 2MTF. We highlight that smoothed velocity fields should be rescaled to obtain unbiased velocity estimates. Comparing the predictions of these models to the observations from a few test sets of peculiar velocity data, obtained from the Second Amendment Supernovae catalogue and the Tully–Fisher catalogues, we find that 2M++ reconstruction provides a better model of the peculiar velocity in the local Universe than the kernel-smoothed peculiar velocity models. We study the impact of peculiar velocities on the measurement of H0 from gravitational waves and megamasers. In doing so, we introduce a probabilistic framework to marginalize over the peculiar velocity corrections along the line of sight. For the megamasers, we find H0 = 70.1 ± 2.9 km s−1 Mpc−1 using the 2M++ velocity field. We also study the peculiar velocity of the galaxy NGC 1052-DF2, concluding that a short ∼13 Mpc distance is not a likely explanation of the anomalously low dark matter fraction of that galaxy.

Revolutionary Approach for Fusion of the Classic, Relativity and Quantum field Theories: Sayed’s Acceleration Equation and Probable Violation of E=mc2

Expansion of the universe is a divine fact in the glorious Quran. The accelerated expansion of the universe is one of the physics mysteries and challenges. This article is a try to find an answer to this ambiguity. A simple fusion and merging of the Newton, Einstein and quantum field equations were carried out to clarify this topic. Innovative equations correlating the acceleration (As), cosmological constant (Ʌ), vacuum energy density (ρ) and distance (d) was deduced. It can be concluded that Sayed`s acceleration constant (As) is proportional to (Ʌ/ρ), (1/8mc2) and (1/πd2). The derivative equation reveals a probable violation of the mass-energy formula (E= mc2); the speed of light might be 12.5% more. This disparity may be due to antimatter contribution; neutrino-antineutrino, β-β+ annihilation and/or a predicted unrecognized very light particle in the atom nucleus. The Sayed`s acceleration constant (As) and (As/Ʌ) ratio were calculated and found to be 6.33825x10-8 m/s2 and 5.7620475x10+44 m3/s2 respectively. Using Sayed`s equations, the calculated acceleration in planck scale is matched with the declared 5.56081x1051 m/s2 value. The The calculated recession velocity at 1 Mpc was found to be 6.5192677 x 108 m/s .and the cosmological constant (Ʌ) is as measured;~1.1x10-52 m-2

General Relativistic Aberration Equation and Measurable Angle of Light Ray in Kerr–de Sitter Spacetime

As an extension of our previous paper, instead of the total deflection angle α, we will mainly focus on the discussion of measurable angle of the light ray ψP at the position of observer P in Kerr–de Sitter spacetime, which includes the cosmological constant Λ. We will investigate the contribution of the radial and transverse motion of the observer which are connected with radial velocity vr and transverse velocity bvϕ (b is the impact parameter) as well as the spin parameter a of the central object which induces the gravito-magnetic field or frame dragging and the cosmological constant Λ. The general relativistic aberration equation is employed to take into account the influence of motion of the observer on the measurable angle ψP. The measurable angle ψP derived in this paper can be applicable to the observer placed within the curved and finite-distance region in the spacetime. The equation of light trajectory will be obtained in such a sense that the background is de Sitter spacetime instead of Minkowski one. As an example, supposing the cosmological gravitational lensing effect, we assume that the lens object is the typical galaxy and the observer is in motion with respect to the lensing object at a recession velocity vr=bvϕ=vH=H0D (where H0 is a Hubble constant and D means the distance between the observer and the lens object). The static terms O(Λbm,Λba) are basically comparable with the second order deflection term O(m2), and they are almost one order smaller that the Kerr deflection −4ma/b2. The velocity-dependent terms O(Λbmvr,Λbavr) for radial motion and O(Λb2mvϕ,Λb2avϕ) for transverse motion are at most two orders of magnitude smaller than the second order deflection O(m2). We also find that even when the radial and transverse velocity have the same sign, asymptotic behavior as ϕ approaches 0 is different from each other, and each diverges to opposite infinity.

Diagnostic Simulations of the Lunar Sodium Tail and Bright Spot

AbstractNumerical simulations of the lunar sodium tail and its bright sodium spot are presented. As an attempt to do reverse engineering to understand the lunar sodium exosphere, we simulated velocity distributions of the sodium tail and its bright spot that emerges in the night sky around new Moon phases. In this work, three physical sodium sources (i.e., photon‐stimulated desorption [PSD], solar‐wind ion sputtering [SIS], meteor impact vaporization [MIV]), the dust anisotropy effect reported by Lunar Atmosphere and Dust Environment Explorer (LADEE), three gravitational sources (i.e., the Moon, the Earth, and the Sun), and variable solar radiation pressure effects are considered. We simulated velocity distributions of the lunar bright spot considering different source contribution ratios and their temperatures in order to find the best initial parameters which can account for the important observed recessional velocity of 12.4 km/s by Mierkiewicz et al. (2006, https://doi.org/10.1029/2006GL027650). We found that the upper limits of Maxwellian temperatures of 1,800 K for the PSD and 2,500 K for the MIV and that the best contribution ratio of the three major sodium sources (i.e., PSD: SIS: MIV) is found at the case of 2: 1: 3 (i.e., MIV dominant). Based on the previous brightness observations of the bright spot, the total production rate of the lunar sodium is estimated to usually vary between 0.4 and 1.3 × 1022/s. We introduce an interesting event in the lunar sodium tail, the Sodium Ring phenomena, which can occur transiently during the total solar eclipse due to the umbra and penumbra effects of the Earth.

The relation between Lyαabsorbers and local galaxy filaments

Context.The intergalactic medium (IGM) is believed to contain the majority of baryons in the universe and to trace the same dark matter structure as galaxies, forming filaments and sheets. Lyαabsorbers, which sample the neutral component of the IGM, have been extensively studied at low and high redshift, but the exact relation between Lyαabsorption, galaxies, and the large-scale structure is observationally not well constrained.Aims.In this study, we aim at characterising the relation between Lyαabsorbers and nearby over-dense cosmological structures (galaxy filaments) at recession velocities Δv ≤ 6700 km s−1by using archival observational data from various instruments.Methods.We analyse 587 intervening Lyαabsorbers in the spectra of 302 extragalactic background sources obtained with the Cosmic Origins Spectrograph (COS) installed on theHubbleSpace Telescope (HST). We combine the absorption line information with galaxy data of five local galaxy filaments from the V8k catalogue.Results.Along the 91 sightlines that pass close to a filament, we identify 215 (227) Lyαabsorption systems (components). Among these, 74 Lyαsystems are aligned in position and velocity with the galaxy filaments, indicating that these absorbers and the galaxies trace the same large-scale structure. The filament-aligned Lyαabsorbers have a ∼90% higher rate of incidence (d𝒩/dz = 189 for logN(H I) ≥ 13.2) and a slightly shallower column density distribution function slope (−β = −1.47) relative to the general Lyαpopulation atz = 0, reflecting the filaments’ matter over-density. The strongest Lyαabsorbers are preferentially found near galaxies or close to the axis of a filament, although there is substantial scatter in this relation. Our sample of absorbers clusters more strongly around filament axes than a randomly distributed sample would do (as confirmed by a Kolmogorov–Smirnov test), but the clustering signal is less pronounced than for the galaxies in the filaments.

A Restless Supermassive Black Hole in the Galaxy J0437+2456

Abstract We present the results from an observing campaign to confirm the peculiar motion of the supermassive black hole (SMBH) in J0437+2456 first reported in Pesce et al. Deep observations with the Arecibo Observatory have yielded a detection of neutral hydrogen (H i) emission, from which we measure a recession velocity of 4910 km s−1 for the galaxy as a whole. We have also obtained near-infrared integral field spectroscopic observations of the galactic nucleus with the Gemini North telescope, yielding spatially resolved stellar and gas kinematics with a central velocity at the innermost radii (0.″1 ≈ 34 pc) of 4860 km s−1. Both measurements differ significantly from the ∼4810 km s−1 H2O megamaser velocity of the SMBH, supporting the prior indications of a velocity offset between the SMBH and its host galaxy. However, the two measurements also differ significantly from one another, and the galaxy as a whole exhibits a complex velocity structure that implies that the system has recently been dynamically disturbed. These results make it clear that the SMBH is not at rest with respect to the systemic velocity of the galaxy, though the specific nature of the mobile SMBH—i.e., whether it traces an ongoing galaxy merger, a binary black hole system, or a gravitational-wave recoil event—remains unclear.

On the kinematic interpretation of cosmological redshifts

We describe what is essentially a correct solution to the kinematic interpretation of cosmological redshifts in standard cosmological model. In the framework of "stretching of space" point of view of the spatially homogeneous and isotropic Robertson-Walker space-time of standard cosmological model, we study so-called "lookforward" history of expanding universe, subject to certain rules, in order to overcome the ambiguity of the parallel transport of source four-velocity along the null geodesic to an observer. We interpret the cosmological redshifts as the accumulation of a series of infinitesimal "relative" spectral shifts along the path of light consequent on recession. The crux of our solution is the kinetic recession velocity of comoving astronomical object, which is always subluminal even for large redshifts of order one or more, so that it does not violate the fundamental physical principle of causality. Our analysis establishes a straightforward kinematic relationship of overall cosmological redshift and kinetic recession velocity, which is utterly distinct from a familiar global Doppler shift formula. A difference of global Doppler velocity and kinetic recession velocity, for redshifts 0.9 ≤ z ≤ 800, is ≥ 0.072c, where a maximum value, 0.187c, is reached at redshifts z = 4.5 - 5.1. A general solution is reduced to a global Doppler shift along the null geodesic. We discuss the implications for the case of a zero-density cosmological model of Milne universe, whereas a correspondence to the more usual special relativity notion of relative speed retains. In Table 1, we are summing up kinetic recession velocities of some typical distant astronomical objects with spectroscopic redshift determinations collected from the literature.

Unique definition of relative speed along the line of sight of a luminous object in a Riemannian space-time

Using a way of separating the spectral shifts into infinitesimally displaced `relative´ spectral bins and sum over them, we overcome the ambiguity of the parallel transport of four-velocity, in order to give an unique definition of the so-called kinetic relative velocity of luminous source as measured along the observer’s line-of-sight in a generic pseudo-Riemannian space-time. The ubiquitous relationship between the spectral shift and the kinetic relative velocity is utterly distinct from a familiar global Doppler shift rule (Synge, 1960). Such a performance of having found a kinetic relative velocity of luminous source, without subjecting it to a parallel transport, manifests its virtue in particular case when adjacent observers are being in free fall and populated along the null geodesic, so that it is reduced to a global Doppler velocity as studied by Synge. We discuss the implications for the instructive case of spatially homogeneous and isotropic Robertson-Walker space-time, which leads to cosmological consequences that the resulting kinetic recession velocity of a galaxy is always subluminal even for large redshifts of order one or more, and thus, it does not violate the fundamental physical principle of causality.

Approximate Bayesian computation for finite mixture models

Finite mixture models are used in statistics and other disciplines, but inference for mixture models is challenging due, in part, to the multimodality of the likelihood function and the so-called label switching problem. We propose extensions of the Approximate Bayesian Computation–Population Monte Carlo (ABC–PMC) algorithm as an alternative framework for inference on finite mixture models. There are several decisions to make when implementing an ABC–PMC algorithm for finite mixture models, including the selection of the kernels used for moving the particles through the iterations, how to address the label switching problem and the choice of informative summary statistics. Examples are presented to demonstrate the performance of the proposed ABC–PMC algorithm for mixture modelling. The performance of the proposed method is evaluated in a simulation study and for the popular recessional velocity galaxy data.

A molecular absorption line survey towards the AGN of Hydra-A

ABSTRACT We present Atacama Large Millimetre/submillimetre Array observations of the brightest cluster galaxy Hydra-A, a nearby (z = 0.054) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1−0), CO(2–1), 13CO(2–1), CN(2–1), SiO(5–4), HCO+(1–0), HCO+(2–1), HCN(1–0), HCN(2–1), HNC(1–0), and H2CO(3–2) absorption lines against the galaxy’s bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds that lie close to the centre of the galaxy and have velocities of approximately −50 to +10 km s−1 relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions, and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a ∼10 km s−1 wide section of the absorption profile over a 2 yr time-scale, most likely caused by relativistic motions in the hot spots of the continuum source that change the background illumination of the absorbing clouds.

On the stellar kinematics and mass of the Virgo ultradiffuse galaxy VCC 1287

ABSTRACT Here, we present a kinematical analysis of the Virgo cluster ultradiffuse galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager (KCWI). We confirm VCC 1287’s association both with the Virgo cluster and its globular cluster (GC) system, measuring a recessional velocity of 1116 ± 2 km s−1. We measure a stellar velocity dispersion (19 ± 6 km s−1) and infer both a dynamical mass ($1.11^{+0.81}_{-0.81} \times 10^{9} \ \mathrm{M_{\odot }}$) and mass-to-light ratio (M/L) ($13^{+11}_{-11}$) within the half-light radius (4.4 kpc). This places VCC 1287 slightly above the well-established relation for normal galaxies, with a higher M/L for its dynamical mass than normal galaxies. We use our dynamical mass, and an estimate of GC system richness, to place VCC 1287 on the GC number–dynamical mass relation, finding good agreement with a sample of normal galaxies. Based on a total halo mass derived from GC counts, we then infer that VCC 1287 likely resides in a cored or low-concentration dark matter halo. Based on the comparison of our measurements to predictions from simulations, we find that strong stellar feedback and/or tidal effects are plausibly the dominant mechanisms in the formation of VCC 1287. Finally, we compare our measurement of the dynamical mass with those for other UDGs. These dynamical mass estimates suggest relatively massive haloes and a failed galaxy origin for at least some UDGs.

Deep spectroscopy in nearby galaxy clusters – V. The Perseus cluster

ABSTRACT Dwarfs are the largest population of galaxies in number in the nearby Universe. Deep spectroscopic data are still missing to obtain a better understanding of their formation and evolution processes. This study shows the results obtained from a spectroscopic campaign in the Perseus cluster. We have obtained 963 new galaxy spectra. We have measured the recessional velocity of the galaxies by using a cross-correlation technique. These data have been used to obtain the cluster membership, the dynamics of the galaxies, and the spectroscopic luminosity function (LF) of the cluster. The cluster membership was obtained by using the peak + gap technique, reporting a total of 403 galaxies as cluster members within 1.4r200. The mean velocity and velocity dispersion of the cluster galaxies are Vc = 5258 km s−1 and σc = 1040 km s−1, respectively. We obtained M200 = 1.2 × 1015 M⊙ and r200 = 2.2 Mpc for this cluster. The clusters members were classified blue and red according to their g − r stellar colour. The velocity dispersion of these two families of galaxies is different, indicating that the blue galaxies can be classified as recently accreted into the cluster. We present the spectroscopic galaxy LF of the cluster. This function turned to be flat: α = 0.99 ± 0.06. In addition, blue and red galaxies show similar densities in the faint end of the LF. This indicates that Perseus does not have a population of red dwarf galaxias as large as other nearby clusters. We have compared the LF of the Perseus cluster with other spectroscopic LFs of nearby clusters and those from cosmological simulations. This comparison shows that the spectroscopic LF of nearby galaxy cluster is far from universal.

The Megamaser Cosmology Project. XI. A Geometric Distance to CGCG 074-064

Abstract As part of the survey component of the Megamaser Cosmology Project, we have discovered a disk megamaser system in the galaxy CGCG 074-064. Using the Green Bank Telescope and the Very Large Array, we have obtained spectral monitoring observations of this maser system at a monthly cadence over the course of two years. We find that the systemic maser features display line-of-sight accelerations of ∼4.4 km s−1 yr−1 that are nearly constant with velocity, while the high-velocity maser features show accelerations that are consistent with zero. We have also used the High-Sensitivity Array to make a high-sensitivity very long baseline interferometric map of the maser system in CGCG 074-064, which reveals that the masers reside in a thin, edge-on disk with a diameter of ∼1.5 mas (0.6 pc). Fitting a three-dimensional warped disk model to the data, we measure a black hole mass of and a geometric distance to the system of Mpc. Assuming a cosmic microwave background-frame recession velocity of 7308 ± 150 km s−1, we constrain the Hubble constant to (stat.) ± 1.4 (sys.) km s−1 Mpc−1.

The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey

Abstract The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey is a blind H i survey of the extragalactic sky behind the northern Milky Way conducted with the ALFA receiver on the 305 m Arecibo Radio Telescope. ALFAZOA Shallow covered 900 square degrees at full sensitivity from 30° ≤ l ≤ 75° and and an additional 460 square degrees at limited sensitivity at latitudes up to 20°. It has an rms sensitivity of 5–7 mJy and a velocity resolution of 9–20.6 km s−1, and detected 403 galaxies out to a recessional velocity of 12,000 km s−1, with an angular resolution of 3.′4 and a positional accuracy between 0.′2 and 1.′7. The survey is complete above an integrated line flux of F H i = 2.0 Jy km s−1 for half the survey, and above F H i = 2.8 Jy km s−1 for the other half. Of the ALFAZOA H i detections, 43% have at least one possible optical/near-infrared counterpart in the literature, and an additional 16% have counterparts that only included previous H i measurements. There are fewer counterparts in regions of high extinction and for galaxies with lower H i mass. Comparing the results of the survey to the predictions of Erdoǧdu et al., and using their nomenclature, ALFAZOA confirms the position and extent in the ZOA of the C7, Cζ, Pegasus, Corona Borealis, and Delphinus structures, but not of the Cygnus void. Two new structures are identified, both connected to the C7 overdensity; one extends to 35°, and the other crosses the ZOA.

Exact recession velocity and cosmic redshift based on cosmological principle and Yang-Mills gravity * * Supported in part by Jing Shin Research Fund and Prof. Leung Memorial Fund of the UMassD Foundation

Based on the cosmological principle and quantum Yang-Mills gravity in the super-macroscopic limit, we obtain an exact recession velocity and cosmic redshift z, as measured in an inertial frame For a matter-dominated universe, we have the effective cosmic metric tensor , where has the operational meaning of time in frame. We assume a cosmic action involving and derive the ‘Okubo equation’ of motion, , for a distant galaxy with mass . This cosmic equation predicts an exact recession velocity, , where and , as observed in the inertial frame . For small velocities, we have the usual Hubble's law for recession velocities. Following the formulation of the accelerated Wu-Doppler effect, we investigate cosmic redshifts z as measured in . It is natural to assume the massless Okubo equation, , for light emitted from accelerated distant galaxies. Based on the principle of limiting continuation of physical laws, we obtain a transformation for covariant wave 4-vectors between and inertial and an accelerated frame, and predict a relationship for the exact recession velocity and cosmic redshift, , where , as observed in the inertial frame . These predictions of the cosmic model are consistent with experiments for small velocities and should be further tested.

H i Spectroscopy of Reverberation-mapped Active Galactic Nuclei

Abstract We present H i 21 cm spectroscopy from the Robert C. Byrd Green Bank Telescope for the host galaxies of 31 nearby active galactic nuclei with direct M BH measurements from reverberation mapping. These are the first published H i detections for 12 galaxies, and the spectral quality is generally an improvement over archival data for the remainder of the sample. We present measurements of emission-line fluxes, velocity widths, and recessional velocities from which we derive H i mass, total gas mass, and redshifts. Combining M GAS with constraints on M STARS allows exploration of the baryonic content of these galaxies. We find a typical M GAS /M STARS fraction of 10%, with a few reaching ∼30%–50%. We also examine several relationships between M STARS , M GAS , M BH , baryonic mass, and morphological type. We find a weak preference for galaxies with larger M GAS to host more massive black holes. We also find gas-to-stellar fractions to weakly correlate with later types in unbarred spirals, with an approximately constant fraction for barred spirals. Consistent with previous studies, we find declining M GAS /M STARS with increasing M stars , with a slope suggesting the gas reservoirs have been replenished. Finally, we find a clear relationship for M BH –M BARY with a similar slope as M BH –M STARS reported by Bentz & Manne-Nicholas. The dwarf Seyfert NGC 4395 appears to follow this relationship as well, even though it has a significantly higher gas fraction and smaller M BH than the remainder of our sample.

An Intuitive Approach to Cosmic Horizons

How far, in space, can we see? And can we see an object whose Hubble recessional velocity exceeds the speed of light? Maybe you’ve thought about these questions before, or perhaps you’ve seen them discussed in the literature or mentioned in the media. With the recent popularity of inflation and Big Bang cosmology, they’re hard to avoid. The discussion that follows is an attempt to resolve some common misconceptions—often seen in the popular literature—concerning the above two questions, and to do so in a way that appeals to kinematical intuition. A simple thought experiment will be used to initiate the discussion and to answer the question, “Can we see objects with faster-than-light recessional velocity?” Hubble’s law, along with a simple assumption about the kinematics of light in expanding space, will be used to derive expressions, customarily derived in a general relativistic context, that allow cosmologists to determine our observational limits and define our cosmological horizons. Some of the results may surprise you. Before we delve into the topic fully, though, let’s first lay some theoretical groundwork.

Галактикалар жиындарының масштабты-инварианттылығы

According to astrophysical observations value of recession velocity in a certain point is proportional to a distance to this point. The proportionality coefficient is the Hubble constant measured with 5% accuracy In this article, the gravitational wave equation was obtained in the form of the oscillation equation from the Einstein theory depending on the coordinates. The numerical results analysis of the system of equations is obtained. For different values ​​of the Hubble parameter, the phase portrait of the dynamical system was taken and the dimensions of the attractors were determined. The expansion of the universe is characterized by the maximum value of the scaling index; these numerical values ​​were taken theoretically in our earlier works.

Gaia Cepheid parallaxes and ‘Local Hole’ relieve H0 tension

ABSTRACT There is an ≈9 ± 2.5 per cent tension between the value of Hubble’s Constant, H0 = 67.4 ± 0.5 km s−1 Mpc−1, implied by the Planck microwave background power spectrum and that given by the distance scale of H0 = 73.4 ± 1.7 km s−1Mpc−1. But with a plausible assumption about a Gaia DR2 parallax systematic offset, we find that Gaia parallax distances of Milky Way Cepheid calibrators are ≈12–15 per cent longer than previously estimated. Similarly, Gaia also implies ≈4.7 ± 1.7 per cent longer distances for 46 Cepheids than previous distances on the scale of Riess et al. Then we show that the existence of an ≈150 h−1Mpc ‘Local Hole’ in the galaxy distribution implies an outflow of ≈500 km s−1. Accounting for this in the recession velocities of SNIa standard candles out to z ≈ 0.15 reduces H0 by a further ≈1.8 per cent. Combining the above two results would reduce the distance scale H0 estimate by ≈7 per cent from H0 ≈ 73.4 ± 1.7 to ≈68.9 ± 1.6 km s−1Mpc−1, in reasonable agreement with the Planck value. We conclude that the discrepancy between distance scale and Planck H0 measurements remains unconfirmed due to uncertainties caused by Gaia systematics and an unexpectedly inhomogeneous local galaxy distribution.

V902 Monocerotis: A likely disc-accreting intermediate polar

Aims. We aim to confirm whether the eclipsing cataclysmic variable (CV) V902 Mon is an intermediate polar (IP), to characterise its X-ray spectrum and flux, and to refine its orbital ephemeris and spin period. Methods. We performed spectrographic observations of V902 Mon in 2016 with the 2.2 m Calar Alto telescope, and X-ray photometry and spectroscopy with XMM-Newton in October 2017. This data was supplemented by several years of AAVSO visual photometry. Results. We confirmed V902 Mon as an IP based on detecting the spin period, which has a value of 2208 s, at multiple epochs. Spectroscopy of the donor star and Gaia parallax yield a distance of 3.5−0.9+1.3 kpc, suggesting an X-ray luminosity one or two orders of magnitude lower than the 1033 erg s−1 typical of previously known IPs. The X-ray to optical flux ratio is also very low. The inclination of the system is more than 79°, and is most likely a value of around 82°. We have refined the eclipse ephemeris, stable over 14 000 cycles. The Hα line is present throughout the orbital cycle and is clearly present during eclipse, suggesting an origin distant from the white dwarf, and shows radial velocity variations at the orbital period. The amplitude and overall recessional velocity seem inconsistent with an origin in the disc. The XMM-Newton observation reveals a partially absorbed plasma model typical of magnetic CVs, that has a fluorescent iron line at 6.4 keV showing a large equivalent width of 1.4 keV. Conclusions. V902 Mon is an IP, and probably a member of the hypothesized X-ray underluminous class of IPs. It is likely to be a disc accretor, although the radial velocity behaviour of the Hα line remains puzzling. The large equivalent width of the fluorescent iron line, the small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests that the X-ray emission arises from scattering.