text:
.). Recently this galaxy was detected during
MeerKAT test observations in preparation for the MeerKAT Fornax Survey Serra
et al. (2016), confirming our ATCA H$I$1.2ex results. FCC 102 has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (4.6$\pm$1.6)$\times$107 M⊙ and a
$M_{\star}$ = (1.6$\pm$0.5)$\times$108 M⊙. The comparison with H$I$1.2ex
belonging to non-cluster galaxies with similar $M_{\star}$ in Fig. 6 shows
that FCC 102 is H$I$1.2ex deficient.

We identify FCC 102 to be part of the NGC 1365 infalling subgroup. It lies
between NGC 1365 and FCC 090 both on the sky and in velocity (see Fig. 12 and
Fig. 13). Furthermore the H$I$1.2ex elongation of FCC 102 is in the same
direction as the H$I$1.2ex elongation of NGC 1365. ‘

### NGC 1436

NGC 1436 is the closest H$I$1.2ex detected spiral to the centre of the cluster
(see Fig 12 and Fig. 13). Ferguson (1989) classify this galaxy as ScII. The
H$I$1.2ex emission associated with NGC 1436 is confined well within the
stellar body suggesting a truncated H$I$1.2ex disc. However, Fig. 3 shows that
the ATCA spectrum compared with that based on GBT data (Courtois et al. 2009)
misses flux from the blushifted part of the disc. This discrepancy might be
due to a faint H$I$1.2ex emission of NGC 1436 which extends over a region
smaller than the ATCA beam in at least some of the blue-shifted channels. This
would cause the average HI column density within the beam to fall below the
sensitivity limit, resulting in a loss of H$I$1.2ex flux in our data. The
H$I$1.2ex spectrum of NGC 1436 spectrum from Schröder et al. (2001) is more
similar to that obtained with the GBT than to ours. The
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ estimated by the ATCA flux is
(5.8$\pm$2.5)$\times$107 M⊙, while the $M_{\star}$ of the galaxy is
(1.6$\pm$0.4)$\times$1010 M⊙. Whether adopting the ATCA or the GBT H$I$1.2ex
flux measurement, NGC 1436 would still be an H$I$1.2ex deficient galaxy (see
Sect.3.2). Similarly, it would still be the (H$I$1.2ex and H21.2ex0pt)
detection with the largest
$M_{\text{H}_{2}}$/$M_{\text{H\scaleto{$I$}{1.2ex}}}$ ratio in Fig. 9.

The high offset from the scaling relation in Fig. 9, the truncated H$I$1.2ex
disc in Fig. 2 and the molecular spiral structure detected by Zabel et al.
(2019) show that NGC 1436 may have gone through a quick interaction with the
cluster environment, which did not affect the inner spiral structure yet.

Furthermore, Raj et al. (2019) found that NGC 1436 appears to be transforming
into a S0 in its morphological evolution. They found spiral arms only in the
central region whereas its outer disc resembles the smooth structure typically
found in the discs of S0 galaxies. The truncated H$I$1.2ex disc agrees with
the observation of a passively-evolving outer optical disc, which is being
shaped by the Fornax environment.

### FCC 090

FCC 090 is classified as a peculiar elliptical galaxy by Ferguson (1989). We
detected H$I$1.2ex emission in FCC 090 for the first time. The H$I$1.2ex
morphology of FCC 090 is elongated towards the south. FCC 090 has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (5.9$\pm$2.1)$\times$107 M⊙ and a
$M_{\star}$ = (1.3$\pm$0.3)$\times$109 M⊙. Its
$M_{\text{H\scaleto{$I$}{1.2ex}}}$/$M_{\star}$ ratio makes it a H$I$1.2ex
deficient galaxy, which lies on the edge of comparison sample of non-cluster
galaxies (Fig. 6).

FCC 090 is part of the NGC 1365 infalling subgroup. Within the subgroup, the
H$I$1.2ex morphology of FCC 090 is the only one which is extended towards the
south; it is the farther galaxy from NGC 1365; it has the highest velocity in
phase space. FCC 090 is also the westernmost galaxy in the triplet of the
aligned H$I$1.2ex disturbed galaxies. Besides FCC 090, this triplet includes
FCC 102 and NGC 1365.

The H$I$1.2ex and molecular distributions (Zabel et al. 2019) are difficult to
compare due to the different resolutions between ATCA and ALMA. The molecular
distribution extends beyond the stellar body showing a tail that points to the
west in projection but it is still within our H$I$1.2ex detection that does
not show any peculiarity in that direction. Our knowledge on H$I$1.2ex in FCC
090 as well as its belonging to the NGC 1365 subgroup, corroborates the idea
of an infalling galaxy which is loosing the external gas envelope.

In the sample of dwarf galaxies studied by Hamraz et al. (2019) FCC 090 is one
out of two outliers in the Fornax cluster with a very blue inner part.
Recently, Zabel et al. (2020) showed that depletion time is shorter than usual
(0.5 Gyr rather than 2 Gyr) which may be a consequence of the environmental
interactions taking place in it.

### ESO 358-G016

ESO 358-G016 is classified as Sdm (edge-on) by Ferguson (1989). It has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (7.4$\pm$2.5)$\times$107 M⊙ and a
$M_{\star}$ = (1.2$\pm$0.7)$\times$108 M⊙. ESO 358-G016 is the only member of
the NGC 1365 infalling subgroup with a regular H$I$1.2ex morphology. Like all
the low mass members of the subgroup, it is a H$I$1.2ex deficient galaxy. It
is also the second closest galaxy to NGC 1365 both on the sky and in phase
space. Raj et al. 2019 suggested that ESO 358-G016 might have experienced
disruptions of the outer disc due to the gravitational potential of the
cluster. If that is the case, some H$I$1.2ex survived in this process.

### ESO 358-G015

ESO 358-G015 is classified as a peculiar Scd-III by Ferguson (1989). It has a
regular H$I$1.2ex morphology, with a systemic velocity close to the
recessional velocity of the cluster. It has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (9.3$\pm$2.8)$\times$107 M⊙ and a
$M_{\star}$ = (7.6$\pm$2.1)$\times$108 M⊙. Fig. 6 shows that ESO 358-G015 is a
H$I$1.2ex deficient galaxy. Furthermore, it is one of the four H$I$1.2ex
detected galaxies that are north of NGC 1399. Raj et al. (2019) identified a
lopsided tail pointing to the centre of the cluster. They also suggested ESO
358-G015 to be a galaxy that is being pulled into the cluster centre, in the
southern direction. The quite regular H$I$1.2ex morphology does not provide
clear support to this hypothesis.

### ESO 358-G051

ESO 358-G051 is classified as SBcd-III by Ferguson (1989). The H$I$1.2ex
distribution is regular and peaks on the optical centre. It is located north
of NGC 1399 and it is the closest H$I$1.2ex deficient galaxy from it
($\sim$0.4 $R_{\mathrm{vir}}$). In general, among all our H$I$1.2ex
detections, only NGC 1427A is closer to NGC 1399. ESO 358-G051 has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (1.0$\pm$0.3)$\times$108 M⊙ and a
$M_{\star}$ = (2.1$\pm$0.5)$\times$109 M⊙. Fig. 6 shows that ESO 358-G051 is a
H$I$1.2ex deficient galaxy.

Raj et al. (2019) marked this galaxy as a recent infaller with strong central
H$\alpha$ emission powered by star formation. Iodice et al. (2019a) observed
an ionised gas distribution extended towards the north. This is the opposite
direction with respect to the H21.2ex0pt elongation detected by Zabel et al.
(2019). However, the H$I$1.2ex distribution does not seem to be disturbed,
perhaps due to the ATCA resolution. Although ESO 358-G051 is a H$I$1.2ex
deficient galaxy, the unresolved H$I$1.2ex morphology does not provide
information about on going interaction with the Fornax environment.

### ESO-LV 3580611

ESO-LV 3580611 is classified as SBm-III by Ferguson (1989). The H$I$1.2ex
morphology shows a lopsided H$I$1.2ex distribution in the northern part of the
system. However, optical and H$I$1.2ex distribution share the same centre. It
has a $M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (1.1$\pm$0.3)$\times$108 M⊙ and a
$M_{\star}$ = (1.0$\pm$0.4)$\times$108 M⊙. ESO-LV 3580611 is also one of the
two H$I$1.2ex deficient galaxies in our sample that is outside the caustic
curves (Fig. 13). Schröder et al. (2001), based on the high deviation of ESO-
LV 3580611 from the Tully-Fisher relation, suggested that this galaxy is
falling into the cluster from the background.

According to Raj et al. (2019), ESO-LV 3580611 may have experienced
disruptions in the outskirts of the disc due to gravitational potential well
of the cluster. Thus, similarly to ESO 358-G016, H$I$1.2ex has survived during
the infall.

### NGC 1437B

NGC 1437B is classified as Sd (edge-on) by Ferguson (1989). The H$I$1.2ex
distribution shows an elongation to the south, while the H$I$1.2ex peak
corresponds to the optical centroid (Fig. 2).

This galaxy is located on the south east of the cluster, close to FCC 323 both
on the sky and in velocity (see Fig. 12 and Fig. 13). Given the small
separation of only 120 kpc with a difference of $\sim$10 km s-1 in velocity,
they might be part of an interacting subgroup of galaxies. NGC 1437B has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (2.4$\pm$0.6)$\times$108 M⊙ and a
$M_{\star}$ = (5.00$\pm$0.01)$\times$109 M⊙ and it is a H$I$1.2ex rich galaxy.

Fig. 9 shows that the Fornax environment has not strongly affected the
$M_{\text{H}_{2}}$/$M_{\text{H\scaleto{$I$}{1.2ex}}}$ ratio yet. On the other
hand, contrary to the case of NGC 1436, the two gas phases are probably
experiencing the same environmental effect. Indeed, although the scales are
different, we found consistency between the southern H$I$1.2ex elongation of
NGC 1437B and the elongation of the molecular morphology detected by Zabel et
al. (2019). Thus, the agreement between its
$M_{\text{H}_{2}}$/$M_{\text{H\scaleto{$I$}{1.2ex}}}$ ratio and the xGASS
scaling relation might be due to a slower evolution with respect to that
taking place in NGC 1436.

Raj et al. (2019) did not observed any hint of optical morphological
transition from the late-type spiral structure, which supports the hypothesis
of a recent infaller. However, they found an optical disturbance in form of
tidal tail, which points to the south in projection and might be due to a
recent fly-by of another galaxy in the cluster. The H$I$1.2ex morphology
agrees with the optical detected tail. If FCC 323 and NGC 1437B belong to the
same subgroup, the former may be the fly-by galaxy that NGC 1437B has
interacted with.

### NGC 1351A

Classified as Sc (edge-on) by Ferguson (1989). The H$I$1.2ex distribution
shows a projected elongation towards the south. It has a velocity similar to
the recessional of the cluster (Fig. 13). NGC 1351A has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (4.7$\pm$1.2)$\times$108 M⊙ and a
$M_{\star}$ = (3.5$\pm$0.8)$\times$109 M⊙. The H$I$1.2ex reservoir is similar
to that of non-cluster galaxies with the same $M_{\star}$ (Fig. 6). NGC 1351A
is isolated both on the sky and in projected phase space (Fig. 12 and Fig.
13). Thus, the H$I$1.2ex asymmetry might be due to the interaction with ICM.
Zabel et al. (2019) detected a slightly more diffuse east side in the
H21.2ex0pt distribution.

### NGC 1437A

NGC 1437A is classified as SdIII by Ferguson (1989). The H$I$1.2ex morphology
is quite regular and its H$I$1.2ex content is comparable with that of non-
cluster galaxies with the same $M_{\star}$ (see Fig.s 2 and 6). NGC 1437A has
a $M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (5.6$\pm$1.3)$\times$108 M⊙ and a
$M_{\star}$ = (1.0$\pm$0.2)$\times$109 M⊙. Although the optical appearance of
NGC 1437A is not regular and the location of its star forming regions suggests
that the galaxy is travelling in a south-east direction (Raj et al. 2019), the
H$I$1.2ex distribution does not show any strong asymmetries. Thus, ram-
pressure and tidal interaction might not be the cause of the asymmetric star
forming regions. However, the poor resolution of the H$I$1.2ex image may hide
H$I$1.2ex asymmetries in projection.

### ESO 358-G060

ESO 358-G060 is a low mass galaxy classified as Sdm (edge-on) by Ferguson
(1989). The H$I$1.2ex morphology is regular. ESO 358-G060 has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (1.1$\pm$0.2)$\times$109 M⊙ and a
$M_{\star}$ = (1.0$\pm$0.6)$\times$108 M⊙. Fig. 6 shows that ESO 358-G060 has
a H$I$1.2ex reservoir comparable with that of non-cluster galaxies with the
same $M_{\star}$. As discussed in Sect.3.2, we pointed out that the Fornax
cluster environment is more effective in altering the gas content for galaxies
with $M_{\star}$ $<$ 3$\times$109 M⊙. This supports the idea that ESO 358-G060
is a likely new Fornax member which has not been affected by the cluster
environment yet. Raj et al. (2019) observed irregular star-forming regions
making the hypothesis of a disruptions due to the gravitational potential well
of the cluster centre, during the fall. However, since the H$I$1.2ex
distribution is not perturbed yet by environmental interactions, internal
feedback might be the cause of the irregular star forming regions. Furthermore
no H21.2ex0pt was detected by Zabel et al. (2019) and it is a dust poor galaxy
as discussed in Sect.4. Overall, this galaxy is forming star with lower rate
than that predicted for galaxies with similar
$M_{\text{H\scaleto{$I$}{1.2ex}}}$/$M_{\star}$ (Fig. 11).

### ESO 358-G063

Classified as Scd (edge-on) by Ferguson (1989). The atomic hydrogen
distribution is more extended to the south-east part of the system. On this
side, H$I$1.2ex contours are more spaced with respect to the opposite side of
the disc where H$I$1.2ex emission seems to be confined within the stellar
body. ESO 358-G063 has a $M_{\text{H\scaleto{$I$}{1.2ex}}}$ =
(1.7$\pm$0.4)$\times$109 M⊙ and a $M_{\star}$ = (1.1$\pm$0.2)$\times$1010 M⊙.
Despite the asymmetries in the H$I$1.2ex distribution, ESO 358G-063 is not
H$I$1.2ex deficient, and the molecular gas detected by Zabel et al. (2019) has
a regular morphology. Thus, the galaxy has just started to interact with the
cluster environment. The idea is supported by its position in projected phase
space (Fig. 13) where the galaxy is just outside the caustic curves. Raj et
al. (2019) found irregular star-forming regions in the ill-defined spiral arms
of ESO 358-G063, which may be signs of minor mergers.

### NGC 1427A

NGC 1427A is classified as Im-III by Ferguson (1989). The H$I$1.2ex morphology
shows a very long tail pointing to the south-east in projection (opposite
direction to the centre of the cluster - we refer the reader to Lee-Waddell et
al. (2018) for a detailed study about the origin of the tail). NGC 1427A has a
$M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (2.1$\pm$0.4)$\times$109 M⊙ and a
$M_{\star}$ = (2.3$\pm$0.5)$\times$109 M⊙. This is the second most massive
H$I$1.2ex galaxy of our sample, which has an H$I$1.2ex content comparable to
that of non-cluster (see Fig. 6). NGC 1427A is the closest H$I$1.2ex detection
to the centre of the cluster (0.2 $R_{\mathrm{vir}}$). Due to its high
velocity (see Fig. 13) it is not clear whether NGC 1427A is already virialised
in the cluster or not. If it is virialised, it may decrease its velocity while
reaching its apocentre. It is the only
$M_{\text{H}_{2}}$/$M_{\text{H\scaleto{$I$}{1.2ex}}}$ upper limit with
$M_{\star}$ $>3\times$109 M⊙ in Fig. 9. Despite the large H$I$1.2ex reservoir
no H21.2ex0pt was detected by Zabel et al. (2019). This may be due to a recent
merger which involved the NGC 1427A progenitors that might have lowered its
metallicity. The H$I$1.2ex-to-H21.2ex0pt conversion might be inefficient to
have a SFR consistent with its $M_{\text{H\scaleto{$I$}{1.2ex}}}$/$M_{\star}$
ratio (Fig. 11).

### NGC 1365

NGC 1365, the large barred spiral galaxy (SBbc(s)I by Ferguson 1989), is the
most massive galaxy in our sample. The optical morphology shows a well defined
spiral structure, three northern arms and two more compressed southern ones.
The H$I$1.2ex morphology (Fig. 2) shows a very prominent extension to the
north of the system and more dense contours corresponding to the two
compressed optical arms. A very detailed study on the structure of NGC 1365 is
made by Jorsater & van Moorsel (1995). They also suggested that the motion of
the galaxy through the ICM can account for its unwinding arms.

NGC 1365 has a $M_{\text{H\scaleto{$I$}{1.2ex}}}$ = (1.5$\pm$0.3)$\times$1010
M⊙ and a $M_{\star}$ = (6.2$\pm$1.3)$\times$1010 M⊙. Fig. 6 shows that NGC
1365 is the only galaxy in our sample which is at the upper edge of the
comparison sample of non-cluster galaxies due to its high
$M_{\text{H\scaleto{$I$}{1.2ex}}}$/$M_{\star}$. Besides evidence of
environmental interactions from its morphology, the strong gravitational
potential appears to have been able to hold a sufficient amount of H$I$1.2ex
to make it comparable with the general behaviour of local galaxies (see also
Fig. 9).

NGC 1365 is the main member of the detected infalling subgroup of galaxies
located to the south-west of the cluster. It is also the only galaxy in the
subgroup with a normal H$I$1.2ex content. The existence of the NGC 1365
subgroup is also supported by Drinkwater et al. (2001a) which found NGC 1365
to be part of a substructure.

There is a H$I$1.2ex hole in the centre of the system where Zabel et al.
(2019) detected warped H21.2ex0pt emission due to the central bar. H$I$1.2ex
absorption was also investigated in Ondrechen & van der Hulst (1989).

## Appendix B

Figure 14: Optical images of the eight H21.2ex0pt-rich H$I$1.2ex-undetected
galaxies (Zabel et al. 2019) for which we evaluated the
$M_{\text{H}_{2}}$/$M_{\text{H\scaleto{$I$}{1.2ex}}}$ ratio (Fig.9). They are
sorted according to increasing $M_{\text{H\scaleto{$I$}{1.2ex}}}$ upper limit.
The g-band optical images come from the Fornax Deep Survey (Iodice et al.
2016; Venhola et al. 2018; Peletier et al. 2020). We show a 5 kpc scale bar in
the bottom-right corner.

license: Creative Commons - Attribution - https://creativecommons.org/licenses/by/4.0/